Review and Critique of the Quantitative Literature Regarding Attitudes toward Consensual Non-Monogamy (CNM)

Abstract

This paper is a review of the recent literature on attitudes toward consensual non-monogamy (CNM). These attitudes are constrained to evaluations of people who practice CNM, CNM relationships, and CNM concepts; willingness to engage in or personal interest in practicing CNM is not included in this review. Relevant published research was located through database searches, as well as by perusing references and citations. Based on over two dozen investigations, it is concluded that average attitudes toward CNM are around neutral, with some slightly negative and some slightly positive. Studies taking a comparative perspective—whereby monogamous couples are pitted against CNM couples—overwhelmingly find more favorable attitudes toward monogamy. This literature supports assertions of the prevalence of monocentrism/compulsory monogamy. Further, some researchers investigated sociodemographic and psychological variables as predictors of CNM attitudes. Considering demographic characteristics, those who identify as monogamous and heterosexual tend to be more negative toward CNM relative to their counterparts, and most of the research suggests there are no gender differences in CNM attitudes. In terms of psychological variables, those reflecting authoritarian ideological values tended to predict CNM attitudes the best. The psychological variables are interpreted within the broader dual-process motivational model of prejudice with attention to authoritarianism and social dominance. To conclude, measurement issues are discussed, existing instruments are critiqued, and recommendations are made for which instruments are appropriate for different research goals. Specifically, the Attitudes towards Polyamory scale is a concise, unidimensional instrument with sound psychometric properties, making it a good general assessment of polyamory or CNM. Created using excellent test construction techniques, the Multidimensional Measurement of Attitudes toward Consensual Non-Monogamy (MACS) is a very promising belief-based CNM attitudes scale with three factors. Finally, directions for future research are discussed with an emphasis on differentiating between beliefs and attitudes as suggested by attitude theory, with most CNM attitude scales conflating the former with the latter.

1. Introduction

Consensual non-monogamy (CNM) is an overarching term for a relationship style whereby participants engage in extra-dyadic relations with the consent of the individuals involved. Such multiple relationships can be romantic, sexual, or both. Sometimes labeled ethical non-monogamy, CNM can take many forms, including, but not limited to, polyamory as well as swinging and open relationships. This is differentiated from covert, extra-relationship intimacy, often called infidelity, affairs, or cheating [1,2]. A key component of CNM appears to be open communication about and agreement to extra-relational sexuality or intimacy. Often discussed in the CNM literature as an identity label, polyamory is a type of CNM defined as “…the practice of having multiple sexual relationships with informed and consenting partners. This included swinging, polyfidelity (a closed relationship consisting of more than two partners), and a variety of open relationship models” ([3], p.24). When presenting CNM to research participants, investigators often use polyamory terminology rather than CNM; the terms are sometimes used synonymously.

In Western society, the dyad is celebrated and sanctioned; marriage is a legal union of two people, initially limited to a man and a woman of the same race, then broadened to allow interracial and same-sex marriage [4,5,6]. Even if legal or religious marriage does not take place, cohabitation between two people is recognized as a binding relational agreement. Indeed, family researchers address cohabitation and marriage relationships, as well as living-apart-together unions, yet often fail to acknowledge the possibility of polyamory or CNM within intimate relationships or family structures (e.g., [7,8]). This valuing of the dyadic relationship has been called compulsory monogamy or mono-normativity and is inherent in systems such as laws, policies, and research [9,10]. Much less attention seems to be paid to intimate relationships that fall outside of the traditional twosome.

CNM or polyamory is not a new concept (e.g., concubines and polygamy are part of history and are present across cultures) but has gained popularity in modern Western society [11,12]. North American representative samples put participation in open or CNM relationships at anywhere from 4% (current) to 20% (lifetime) [2,12,13,14]. One study found of the 11% who had a history of polyamory, only 30% would engage in it again [15]. Moors and colleagues [15] created a desire to engage in polyamory index and found that about 17% of their representative sample had a desire to engage in polyamory. A substantial number (12%) identified open relationships as their ideal relationship status [13].

Despite relatively high rates of engagement in or desire for polyamory or CNM, Moors and colleagues [15] found only 6.5% of their sample reported knowing people who engaged or are interested in polyamory. Knowing someone from a particular group typically reduces prejudice toward that group (i.e., the contact hypothesis [16]). Despite this, only 14% indicated that they have respect for people who engage in polyamory (but they would not do it themselves). Moors and colleagues [15] interpreted this as evidence of the stigmatization of polyamory and CNM.

CNM and polyamory are stigmatized behaviors and identities, it is argued, through structural and societal privileging and normalization of monogamy [4,17,18]. There is a robust body of literature suggesting that people who engage in CNM experience prejudice and discrimination. A large-scale survey found that about a quarter of polyamorous participants indicated that they had been discriminated against in the last decade due to their polyamory [19]. In a review of the polyamorous parenting literature, Klesse [9] reported polyamorous families with children experience fear of bullying, stigma, and legal discrimination. Some responses to such stigmatization include concealing (i.e., passing as monogamous) or assertive coming out (i.e., demanding recognition and inclusion); this is similar to same-sex couple stigma management [9]. This stigmatization has been documented in relation to work settings, family circles, and friendship networks [20,21]. Critically, stigma, prejudice, and discrimination have been felt in healthcare domains [22,23,24,25].

Despite the growing literature on the experiences of CNM people, there has been little written about attitudes toward CNM. In their critical reflection on research and theory regarding CNM in the social sciences and humanities, Barker and Langridge [26] failed to mention attitudes toward CNM. Much of the research has focused on the experiences of polyamorous CNM people, areas such as agreement and rules, comparing CNM with infidelity, as well as CNM identities, intersectionality, and queer theory application [26]. Scoats and Campbell [27] also spoke about the state of psychological knowledge about CNM but focused less on attitudes toward it and more on the stigma experienced by CNM practitioners. Enacted stigma involves experiences or feelings of derogation perceived by the person with the stigmatized attribute [28]; while valid and worthy of consideration, enacted or anticipated stigma experiences do not necessarily speak to the state of others’ attitudes toward CNM. One issue with enacted stigma is that, because of pervasive mono-normativity, it is logical that most CNM practitioners would have experienced at least one microaggression or rejection. Negative experiences are usually weighed more heavily than positive [29], and, as a result, negative reactions of others could be overemphasized and give the impression of pervasive negative CNM attitudes. However, in a large (N = 1000) convenience sample of CNM practitioners, the average response to an index of past CNM stigmatizing experiences (e.g., people have made hurtful comments re: my CNM relationships) was at the scale midpoint (i.e., neither agree nor disagree [30]). Thus, reported enacted stigma by CNM practitioners may not be a good marker for social perceivers’ attitudes toward polyamory or CNM. By assessing the attitudes of social perceivers directly, we can gauge support for or rejection of CNM more accurately and gain a greater understanding of how to foster positive attitudes. Consequently, the goal of the current paper is to review and critique the literature on attitudes toward CNM.

To address this broad goal, the attitudes of others toward those who practice CNM are the focus of this paper. First, how attitudes are measured, generally, is described to provide a context to interpret existing research and for measurement issues discussed later. Constraining the literature to quantitative investigations, published papers are reviewed where the overall valence (i.e., positive, neutral, or negative) of attitudes toward CNM and CNM practitioners by non-CNM perceivers are presented. Within this literature, many studies investigated demographic and personality correlates of CNM attitudes. Hence, a summary of individual difference predictors of CNM attitudes is described. A theoretical integration that frames these individual difference findings is offered. Finally, scales created to measure CNM attitudes are described and critiqued; suggested uses of the scales and recommendations for future research are made.

For the purposes of identifying the literature addressing attitudes toward CNM by non-practitioners, academic databases were searched (e.g., PsycInfo) using a variety of search terms such as “CNM”, “consensual nonmonogamy”, “polyamory” plus “attitudes”, and “beliefs”. Relevant quantitative articles were identified; these were constrained to investigations where the topic of study involved attitude and belief constructs assessing opinions of non-CNM practitioners as opposed to felt stigma perceived by CNM practitioners. This differentiated attitudes from felt stigma [31]. The literature was also identified by perusing the reference sections of recent papers (e.g., [20,23]) and earlier related literature reviews (e.g., [26,27]). Studies conducted prior to 2000 were not considered as older studies are discussed elsewhere (see [32]). Identification of relevant articles also involved looking at who cited key papers (e.g., Johnson et al. [33]) and influential authors in the field [e.g., Cohen, Moors]. Generally, the literature review procedures outlined by Paré and Kitsiou [34] were followed.

What Are Attitudes and Why Are They Important?

An attitude is an evaluation of a person, object, idea, behavior, etc., that is held by a social perceiver. In relation to person perception, we speak about attitudes toward people of different minority groups: ethnicities, races, sexual orientations, gender identities, etc. When studying attitudes, minority group attitude targets (i.e., outgroup members) are often rated by those who are of the majority group (i.e., ingroup).

Attitude scholars [35,36,37] suggest attitude assessment takes the form of semantic differential scales: “My attitude toward object X is good–bad, positive–negative, awful–nice, unfavorable–favorable”. There are variations on this type of semantic differential scale (e.g., “My attitude toward object X is positive, agree-to-disagree”) as well as feeling thermometers (e.g., Consider your general opinion of object X. How do you feel about object X? 0–100 cold-to-warm). However, presented to social perceivers, these scales assess overall evaluations of the target.

Overall evaluations are theoretically determined by a set of salient beliefs [35,36,37]. Salient beliefs are individual ideas about or perceived characteristics of the attitude object; thus, positive and negative ideas of an attitude object can be held simultaneously. For example, consider “CMN practitioners are happy” and “CMN practitioners are more likely to have an STI”; a single individual can endorse both beliefs simultaneously despite one being a negative and the other positive. Social perceivers are thought to engage in a type of cognitive algebra with these beliefs in order to produce an attitude (e.g., weighing the STI belief more heavily than the happiness belief). Beliefs and attitudes are thought to determine intention; intention is an indicator of willingness or likelihood to engage in a behavior (e.g., potentially discrimination or an ally action). These types of semantic differential scales or belief-based agreement measures are best described as explicit measures. That is, they require conscious thought or cognitive effort to produce a rating, and they can be influenced by demand characteristics and self-presentation concerns (e.g., wanting to please the researcher, not wanting to appear prejudiced).

Another type of attitude measure is called an implicit measure [37]. Usually, this is a reaction-time-based assessment whereby participants respond to words or pictures, usually describing groups (e.g., CNM practitioners, gay men) paired with positive and negative descriptors (e.g., good, immoral). This process is thought to be more automatic and less influenced by socially desirable biases than explicit self-report measures. The unconscious attitudes measured by this process are thought to reflect more experiential, associative learning acquired through cultural sources rather than individual, conscious attitudinal preferences, per se [38]. This may explain why implicit and explicit attitudes are not perfectly congruent. That is, different cognitive processes are active in producing explicit and implicit attitude responses [38]. The two types of attitude measures tend to be correlated modestly with each other, and both predict behavior modestly [39,40]. Most of the CNM attitude literature is based on explicit attitude measurement, although there is a growing body of studies that employ implicit attitude outcomes.

2. Are Attitudes toward CNM Positive or Negative?

How one answers this question depends on how one interprets the extant research in this area. If reading the literature where people who are CNM practitioners report their interpretations of and experiences with others, one might conclude that attitudes are pervasively negative [2,23,30]. However, the different ways attitudes have been measured and different research methodologies used to measure social perceivers’ attitudes toward CNM complicate the answer as to whether CNM attitudes are positive or negative.

2.1. Attitudes toward CNM Are Tepid

2.1.1. Studies Suggesting CNM Attitudes Are Negative

Only a few researchers have used the traditional semantic differential attitude assessment when measuring CNM attitudes. Using a classic attitudinal evaluation measure (e.g., good/bad, like/dislike), Burris [41] found that university student participants rated a polyamorous target slightly negatively. Like Burris, Thompson and colleagues [42], as well as Rodrigues and colleagues [43], also found participants, overall, to be slightly negative. However, Rodrigues et al. [44] found participants to be neutral to slightly positive on two general favorability items. These studies using classic attitude scales, on balance, suggest attitudes toward CMN are slightly negative.

Three aggregated belief instruments have been constructed that define attitudes by underlying beliefs rather than by overall evaluations [35,36,37]. Johnson et al. [33] designed an Attitudes towards Polyamory scale using seven polyamory-related belief items and found attitudes were neutral-to-slightly negative. After changing the target topic from polyamory to non-monogamy on Johnson et al.’s Attitudes towards Polyamory scale, Thompson et al. [45] also found that average ratings produced neutral-to-slightly negative ratings. Stephens and Emmers-Sommer [46] found that attitudes were slightly negative but almost neutral on a CNM Attitudes scale constructed by Cohen and Wilson [47]. Barrada and Castro [48] also found university student participants slightly negative (i.e., below the midpoint) on the Cohen and Wilson [47] scale. Further, Moors, Conley, Edelstein, and Chopik [49] created a six-item, belief-based Attitudes toward CNM scale; their sample averaged slightly negative ratings on this instrument. Ka et al. [50] replicated this finding using the same Attitudes toward CNM scale. These findings suggest attitudes toward CNM, measured by these three aggregated belief scales, are neutral-to-slightly negative.

To gauge attitudes from a different perspective, some studies have presented participants with scenarios and had them rate the CNM targets or their CNM relationship on specific attributes such as emotions, relationship quality or satisfaction, and morality. For example, Rodrigues et al. [43,51] assessed the dehumanization of monogamous versus CNM targets by asking social perceivers to rate emotions experienced by target people who were described in vignettes. In both investigations, CNM targets received ratings of experiencing “less human” or primary emotions (i.e., emotions expressed by both animals and humans, such as fun or tension) at or above the midpoint. In terms of experiencing “uniquely human” or secondary emotions (i.e., emotions only expressed by humans, thus indicating higher evolutionary functioning; emotions such as hope or shame), CNM targets were rated at or below the midpoint. This is evidence of negative evaluation of CNM targets; the authors call this dehumanization of CNM targets (i.e., as they are perceived as more animalistic and less human in their emotional lives).

Researchers have measured attitudes by having participants rate attributes or character traits of CNM vignette targets. For example, Rodrigues and colleagues [43] found that those described in an open or polyamorous relationship were rated negatively or neutrally (i.e., around or below the scale midpoint) in relation to promiscuity, morality, sexual satisfaction, and relationship commitment. Matsick et al. [52] assessed CNM perceptions on 18 characteristics; the ratings of individuals involved in the different CNM relationships were unflattering (e.g., high on dirty and selfishness while low on morality and relationship satisfaction).

Rather than assessing attitudes toward the CNM person, a couple of studies have investigated perceptions of CNM relationships. The outcome measures are often attributes of the relationship (e.g., this relationship is meaningful or comfortable), or sometimes attributes of the CNM couple are assessed (e.g., intelligence of the couple). Specifically, Conley et al. [53] found that CNM relationships were generally rated on the negative end of the scale (i.e., below the midpoint) on a variety of individual relationship qualities (e.g., relationship maturity, relationship promotes respect) as well as aggregated categories (e.g., relationship acceptability). Following a similar design, Burleigh et al. [54] found CNM ratings to be somewhat negative; ratings of the couple in an open relationship were below the midpoint for being happy, intelligent, kind, unselfish, committed, emotionally secure, in love, romantic, satisfied, and trustworthy, although many assessments hovered around the midpoint. Albeit a fine distinction, Burleigh et al. [54] further assessed ratings of the couple’s relationship—as opposed to ratings of the CNM people—and found ratings to be negative (e.g., relationship as immature, unsafe, immoral, unreliable, unnatural, uncomfortable, and lacking meaning). Balzarini et al. [55] also found that monogamous participants rated individuals in CNM relationships as promiscuous and likely to have an STI (i.e., both above the scale midpoint).

Collectively, these studies [33,41,42,43,44,45,46,48,49,50,51,52,53,54,55] suggest attitudes toward CNM targets are mildly negative. Attitudes were measured using a variety of techniques, including classic semantic differential scales; belief-based aggregated general instruments, like the Attitudes toward Polyamory scale; personal attributions about CNM practitioners (i.e., the couple), including their emotional experiences, characteristics, and traits; and attributions about CNM relationships, generally. Considering these studies and the multiple methods used to assess explicit attitude outcomes, one might conclude that CNM attitudes are negative. Yet, the literature is not consistently negative.

2.1.2. Studies Suggesting CNM Attitudes Are Neutral or Positive

In contrast to this substantive literature suggesting that CNM attitudes are slightly negative, there is a body of evidence supporting neutral-to-positive attitudes toward CNM. For instance, Cardoso et al. [56] further validated Johnson et al.’s [33] beliefs about polyamory instrument. Their Portuguese sample expressed more favorable polyamory beliefs compared to Johnson et al. [33], with all items averaging over 5 (slightly agreeing with the positively phrased items and slightly disagreeing with the negatively framed statements) on the 7-point scale (an exception was a religion item which was subsequently deleted). Flicker and Sancier-Barbosa [57] also used the Johnson et al. [33] Attitudes towards Polyamory scale and found attitudes, overall, to be around neutral.

In their validation study introducing their CNM Attitudes scale, Cohen and Wilson [47] found that the approximate average of their two samples indicated a neutral attitude, with the overall average being at the scale mid-point. Using a modified version of Cohen and Wilson’s [47] belief-based scale, Powers et al. [58] found a sample of US adults were generally positive in attitudes toward consensual non-monogamy. Also, using the Cohen and Wilson [47] scale, St. Vil and Giles [59] found participants were neutral, on average. Moors et al.’s [60] sample of sexual minority participants was precisely at the midpoint using the Attitudes toward CNM scale [49]. In short, aggregated belief instruments have also produced neutral or positive ratings of CNM overall.

Using attribute or trait assessments, some studies have also found positive judgments of CNM targets exist. In a vignette description, Grunt-Mejer and Campbell [61] found participants rated polyamory, open, and swinging couples positively—with an average above the scale midpoint—in terms of relationship satisfaction, cognitive abilities, and morality. In a sample of therapists-in-training, Grunt-Mejer and Lys [62] found polyamorous and open-relationship partners were rated positively, on average, on morality, competence, and relationship satisfaction scales consisting of 18 traits or characteristics. Thompson and colleagues [63] replicated this finding. Rodrigues, Aybar Camposno, and Lopes [44] found participants to be neutral to slightly positive in relation to attributions such as trustworthiness, morality, and sexual satisfaction for open and polyamorous partner vignettes. St. Vil and colleagues [64] also found CNM couples were rated slightly positively on an index of relationship quality. Cohen [65] found polyamorous and open relationships were rated favorably in terms of relationship satisfaction (i.e., over 4 on a 5-point scale). Thus, many studies using attributes demonstrate neutral or positive ratings of CNM [44,61,62,63,64,65].

In one of the only studies to assess social distance tolerance, which is the willingness to have the target in a close relationship with oneself, Balzarini et al. [55] found that none of the CNM targets were below the scale midpoint (i.e., the average was tolerating targets between 3 = neighbor and 4 = coworker on the 7-point scale) by monogamous participants. Approaching attitudes from a different perspective, Séguin [66] analyzed spontaneously produced comments about polyamory on three websites; she identified five major themes based on these comments. Two positive and three negative themes were identified, which is why this study is often cited as evidence of negative attitudes toward CNM. However, the most prevalent theme was positive (i.e., polyamory as valid and beneficial). Thus, this study can be interpreted as supporting the idea that positive and negative attitudes exist in the cyber-sphere. This study is also unique in that it addresses spontaneously offered comments, while most of the current literature consists of investigations soliciting attitudes or beliefs.

In sum, a close examination of several studies using samples of (predominantly) monogamous social perceivers suggests attitudes toward CNM targets or topics are neutral or positive [44,47,55,56,57,58,59,60,61,62,63,64,65,66]. These studies used aggregated scales (e.g., CMN Attitudes scale), character or trait attributions (e.g., relationship satisfaction), and some unique attitudinal outcome assessments (e.g., social distance) and found positivity toward CNM. Thus, while there is definitely evidence of negativity, attitudes toward CNM have not been found to be uniformly nor absolutely negative. At times, a study can be interpreted as supporting the existence of positive and negative attitudes (e.g., [66]). One thing that is consistent across studies of monogamous participants’ ratings of CNM targets is that attitudes were never strongly positive or negative. All attitudes—whether positive or negative—tended to be close to the mid-point. From an absolute or valence perspective, attitudes toward CNM can be described as tepid or temperate (see Appendix A for a table providing more details of the various study findings).

2.2. CNM Relative Attitudes

2.2.1. CNM Compared to Monogamy

Thus far, explicit attitudes, beliefs, and judgments from an absolute perspective have been discussed; that is, what was the absolute rating of the CNM target? A common paradigm used to explore attitudes compares CNM relationships to a monogamous relationship (i.e., with the monogamous relationship used as the reference group). This type of attitudinal study speaks to attitudes as “-isms”; that is, the preference for one group over another (e.g., akin to sexism or heterosexism; the term “non-monogamy” illustrates the primacy of monogamy itself. Parallel terms such as “non-male”, “non-heterosexual”, or “non-white” would not be acceptable in modern society).

Overall, the comparative studies find that monogamous couples are judged more favorably than CNM targets [43,44,51,53,54,55,61,62,63,64,65]. Most of these studies have used attribute ratings rather than overall evaluation attitudes. Some of these attributes can be construed as beliefs—measured individually (e.g., one item) or in aggregate (e.g., an index of similar beliefs). For example, CNM couple targets have been rated as more likely to have an STI than monogamous couple targets [44], and Grunt-Mejer and Lys [62] found that polyamorous and swinging couples were rated less positively on average compared to monogamous couples on aggregated morality, competence, and relationship satisfaction characteristics, respectively.

Other attitudinal-type comparisons also support that monogamous couples are held in higher esteem than CNM couples. Using a social-distance dependent measure, monogamous participants were willing to be closer to monogamous targets (i.e., have target as a close friend) compared to polyamorous targets (i.e., have target as a neighbor/co-worker [55]). Therapists-in-training received scenarios describing different types of couples (CNM, monogamous) seeking psychotherapeutic treatment for different problems; these participants were likely to attribute couple problems (e.g., depression, alcohol abuse) to couple composition when the couple was described as polyamorous (30%) or swinging (34%) compared to monogamous (4%) [62]. These attributions were produced spontaneously in a written analysis of the couple by the participant; thus, this was an indirect attitude assessment [62]. This finding might be explained by “the devil effect”, which is the opposite of the social cognitive bias of the halo effect [67], whereby a (negative/positive) perception of a target in one area affects perceptions of the target in other areas (see [55]). In essence, a social perceiver may conceptualize knowledge of a target’s non-monogamous relationship status as a central trait. This central trait colors perceptions of many other target traits, behaviors, etc., despite being irrelevant (e.g., paying taxes on time [53]).

Another comparative assessment involves implicit attitudes. Thought to reflect associative knowledge, implicit measures of attitude assess participant reaction time; these reaction times can be compared to a reference group. Three studies have investigated attitudes toward CNM using the implicit attitude methodology. Thompson, Bagley, and Moore [45] found a strong preference for monogamy relative to CNM. This attitude assessment is not necessarily about attitudes toward CNM persons. This implicit attitude process may be assessing monogamy and CNM concepts as the stimuli used to provoke participant responses included words (i.e., “exclusive relationship” and “going steady” for monogamy, while “open relationship” and “partner swapping” represented CNM). Images were also used to represent monogamy and CNM visually (e.g., stick figures holding hands with two vs. three people depicted; these represented monogamy and CNM, respectively). These images were paired with positive and negative words, and the response time was noted. Kenyon et al. [68] replicated this implicit attitude procedure and found the majority of participants (over 90%) demonstrated a preference for monogamy over CNM.

In a follow-up study, Thompson, Moore, Haedtke, and Karst [42] examined monogamy and CNM implicit attitude reaction times independently of each other (i.e., comparing the scores to zero rather than each other). Consistent with mono-normativity, there was a strong association between monogamy and positive descriptors (e.g., good, happy). Further, Thompson et al. [42] found that attitudes toward CNM were neutral using this implicit association task. Again, these assessments were not about particular people but rather assessed CNM category concepts like “group sex”, “open marriage”, and “group marriage” and images of couples or threesomes. Regardless, this study can be interpreted as evidence of mono-normative preference, given monogamy was strongly associated with positivity while CNM involved neutrality.

Collectively, the comparative studies find that monogamous couples are judged more favorably than CNM targets [42,43,44,54,55,61,62,63,64,65,68]. This finding is consistent across the assessment methodology used (i.e., measuring outcomes using explicit and implicit measures). In most of the literature, comparative attitudes are defined using beliefs, and, usually, the attitude object is “the couple” (e.g., “Fred and Ginger have an open relationship”) or a CNM concept (e.g., “group sex”) rather than an individual (e.g., “Fred”).

2.2.2. Types of CNM Compared to Each Other

Another set of comparative studies involves monogamy being juxtaposed with different types of CNM (e.g., monogamy vs. polyamory vs. open relationships). Sometimes non-consensual non-monogamy (i.e., infidelity) was included as a comparison group. With monogamy or monogamous couples rated most positively, infidelity—when included—was rated the most negatively [61,62,64]. Polyamory or polyamorous couples were usually rated the same as open relationships [41,43,62,63,64] but not always [52,55,61]. If included as a comparison group, swinging or group sex was usually judged more favorably than infidelity [61,62] but not necessarily as positively as polyamory and/or open relationships [52,63]. When comparing polyamory and open relationships to swinging, the findings have been inconsistent (e.g., [61] vs. [62] and sometimes different within a single investigation, contingent upon the dependent measures, e.g., [55]). Although monogamy is clearly preferred and infidelity is clearly shunned, it would be premature to conclude a preferred CNM attitudinal order with regard to polyamory, open relationships, group sex, and swinging (cf., [1,27,69]).

3. What Predicts CNM Attitudes?

Aside from determining absolute attitudinal levels and comparing attitudes of different types of CNM to attitudes toward monogamy, there is an emerging body of literature on correlates of attitudes toward CNM. The goal of identifying traits and characteristics of those who hold negative attitudes is to understand, predict, and ameliorate prejudice (i.e., by identifying those most likely to be prejudiced at whom to target intervention efforts). Different sociodemographic characteristics, as well as psychological variables, have been investigated as predictors of CNM attitudes depending on the theoretical orientation presented by the scholars.

3.1. Differences Based on Sociodemographic Characteristics

3.1.1. Relationship Orientation

Thus far, the studies described address attitudes toward CNM by the majority group (i.e., usually heterosexuals, usually participants who identified as monogamous). A few studies have investigated the attitudes of those who are CNM practitioners and contrasted these attitudes with those of non-practitioners. Specifically, Balzarini et al. [55] had participants who had different relationship types (i.e., monogamous and three different CNM groups) rate targets of different relationship types on social distance, promiscuity, and STI likelihood outcome variables. All participants, regardless of their own relationship type, rated monogamous targets more positively (i.e., have closer relationships with them, lower perceived promiscuity, and a lesser likelihood of having an STI). However, the assessment of CNM targets was more favorable when ratings were made by participants in CNM relationships relative to monogamous participants, particularly for social distance; these CNM participants also produced lower promiscuity target ratings and lower likelihood of having an STI compared to monogamous participants. Similarly, Stephens and Emmers-Sommer [46] found monogamous participants were more negative than CNM participants on Cohen and Wilson’s [47] scale. That CNM social perceivers rate CNM targets more positively than monogamous social perceivers is consistent with ingrouping/outgrouping processes of social identity theory [70].

In contrast to Balzarini et al. [55], Cohen [65] found no interaction between participant relationship type and target relationship type for the outcome variable (i.e., relationship satisfaction). However, Cohen [65] found that monogamous participants rated all couple types (monogamous, polyamorous, or open) less favorably compared to polyamorous participants on relationship satisfaction. In a larger study, participants who were current as well as past CNM practitioners were more favorable in beliefs about CNM than those who were monogamous [71]. Perhaps indirectly related to relationship orientation, Skakoon-Sparling et al. [71] found that those who were in a romantic relationship were more favorable than those who were single on their measures of attitudes toward CNM. Similarly, those who were more sexually experienced were more positive than those who were less sexually experienced. Perhaps those who are more relationship-experienced (e.g., in more relationships, broader sexual activity) are more relationship-positive, generally.

More research needs to be conducted to tease apart what mechanisms underlie these attitudinal differences between people who identify as monogamous and those who identify as CNM practitioners. It is possible that ingrouping/outgrouping processes are at play, as well as potential CNM stigma/internalized prejudice [31,70]. Another possible explanation is that those who engage in CNM may simply have more favorable attitudes toward romantic relationships, per se, than monogamous people. In addition, the different dependent variables used in these studies (e.g., belief scales and social distance ratings) do not allow for easy comparison.

3.1.2. Sexual Orientation

Another key person-characteristic area where there are differences in CNM attitudes involves the sexual orientation of the participant. A few authors have compared the attitudes of heterosexual participants to those of sexual minority status and found differences in CNM ratings. On the CNM Attitude scale [47], sexual orientation minorities were significantly more favorable than heterosexual participants. Participant sexual orientation was a significant multiple regression predictor of the CNM Attitude scale, whereby those with a heterosexual orientation had more negative attitudes than those with a sexual minority sexual orientation [48,59]. On a 16-item belief scale, Skakoon-Sparling et al. [71] found sexual minority participants more favorable than heterosexual participants. On indices of relationship satisfaction, cognitive abilities, and morality, Grunt-Mejer and Campbell [61] found an interaction between participant sexual orientation and target relationship type such that queer participants rated hypothetical monogamous and CNM couples the same and quite positively, relative to heterosexual couples who rated the hypothetical CNM couples more negatively (and all participants rated infidelity scenario the most negatively). Sexual orientation minorities may be more positive than heterosexual people because they identify with CNM practitioners as a type of sexual minority, as well (i.e., via an ingrouping process [70]). Alternatively, sexual minorities may be more positive toward CNM than heterosexuals because CNM has been a practice in the queer community historically [14].

3.1.3. Gender

Gender is another potential demographic predictor of CNM attitudes. In their methodological review, Sizemore and Olmstead [32] suggest that men are more favorable toward CNM than women, citing Moors et al.’s [49] finding that participant gender was a significant multiple regression predictor of their Attitudes toward CNM scale. Other research supports that men express more positive attitudes toward CNM concepts compared to women (i.e., [42,59,72,73]). In contrast, a few studies support the opposite: that women are more positive toward CNM than men (i.e., [63,74,75]). Of these latter studies, one had mixed findings (i.e., no gender effects on some dependent variables [74]), and one had a very weak effect size [63]. If any particular study finds that gender differences exist in attitudes toward CNM, it is likely a function of methodology (e.g., operationalization of attitudes with implications for the self or for the ingroup).

Most studies have found no gender differences or have found gender irrelevant to the prediction of CNM attitudes [41,45,47,54,60,65,71,74,76,77,78,79,80]. Most of these studies used vignette assessments, while some used aggregate scales. While not specifically assessing gender differences, Conley, Moors, Matsick, and Ziegler [53] separated their analyses by male and female participants; both groups demonstrated a similar preference for monogamy over CNM effects. Generally, gender differences do not exist in attitudes toward CNM [69].

3.1.4. Religion

One variable investigated in relation to prejudice toward sexuality topics is religiosity or religious affiliation of the social perceiver (e.g., [81]). As a sociodemographic variable, religiosity has been investigated in relation to CNM attitudes in only a few studies. Cragun and Sumerau [72] found religiosity differences in feeling thermometer ratings of polygamists, whereby those with more literal views of the Bible were more negative than those who view the Bible as myth. Ford and Hendrick [77] found differences based on religious affiliation whereby Jews and non-religious therapists were less restrictive in endorsing compulsory monogamy than other denominations (i.e., Catholic, Protestant, and others). Johnson et al. [33] found that religious fundamentalism correlated 0.56 while a single-item measure of religiosity correlated 0.43 and 0.48 with their Attitudes towards Polyamory scale [78], indicating moderately strong relationships between religiosity and beliefs about CNM. Grigoropoulos et al. [74] also found that religiosity (measured by religious behavior: attending services, praying) correlated moderately (r = 0.45) with the Johnson et al. [33] instrument. However, religiosity correlated more weakly with beliefs about polyamorous people as parents (i.e., equality rights, competency, and children’s welfare; rs = 0.17–0.37). In short, religiosity—measured in various forms—correlates modestly with CNM attitudes. Those with more liberal religiosity or ideology tend to be more favorable toward CNM.

3.1.5. Political Orientation

From a macro perspective, politics have substantial effects on sexuality policies (e.g., abortion, same-sex marriage); at a more micro level, political orientation is related to sexual conservatism (e.g., [82]). Johnson et al. [33] found that political orientation correlated modestly with their Attitude toward Polyamory belief-based scale (also see [78]). Grigoropoulos et al. [74] found that political orientation correlated weakly but consistently with several measures of attitudes toward CNM and monogamy. Ford and Hendrick [77] found therapists with a very liberal political orientation express less agreement than those with other political positions (e.g., liberal, moderate, and conservative) on an item assessing the importance of relational monogamy. Balzarini et al. [55] included political orientation in their multiple regression equation predicting social distance tolerated for CNM targets. Across these studies, political orientation shared between 4 and 16% variance with CNM attitudes, suggesting political orientation is a modest predictor of attitudes with greater liberalism related to more favorable attitudes.

3.1.6. Summary of Predictiveness of Demographic Characteristics

In sum, demographic characteristics of social perceivers can be predictive of CNM attitudes. Gender appears to be mostly unrelated to such attitudes, whereas relationship orientation and sexual orientation appear to be relatively strong predictors of CNM attitudes. Political ideology and religiosity also appear predictive of CNM attitudes. Much of these sociodemographic findings can be interpreted within a social identity framework, but this explanation has yet to be tested empirically. These conclusions need to be considered tentatively given that only a very few studies have investigated these sociodemographic variables (although gender has been investigated more than the other person-characteristics variables discussed).

3.2. Personality and Individual Differences

3.2.1. Authoritarianism and Social Dominance

Individual differences and personality characteristics influence a person’s perception and related attributions [70]. Authoritarianism and social dominance have been investigated substantially in relation to prejudice and discrimination against many target groups. Authoritarianism and social dominance have been characterized as personality dimensions but are more aptly considered ideological attitudes reflecting motivational values, which moderate the influence of personality traits [83,84,85]. Further, Sibley and Duckitt [85] demonstrated that personality traits (i.e., openness to experience and agreeableness) are moderated by authoritarianism and social dominance in the prediction of prejudice. In their dual-processing model, Duckitt and Sibley [84] describe authoritarianism as “the world is a dangerous place” and social dominance as “the world is a competitive jungle” orientations toward society. Authoritarianism is thought to be largely heritable, while social dominance is mainly influenced by the environment [86]. Many studies have investigated the roles of these ideological attitudes and individual differences in sexual minority prejudice (e.g., [87,88]).

A few studies have explored the relationships between authoritarianism and authoritarian personality-related constructs with attitudes toward polyamory. For instance, Johnson et al. [33] found that right-wing authoritarianism correlated moderately strongly with their Attitudes towards Polyamory scale (r = 0.65; more authoritarian, more negative attitudes). Flicker and Sancier-Barbosa [57] assessed the relationship between Johnson et al.’s [33] Attitudes towards Polyamory scale and a social conformity scale (an alternative measure of authoritarianism). They found that social conformity was the most strongly related to polyamory attitudes (r = 0.49) out of a variety of authoritarian-related constructs (e.g., uncertainty, trust, desire for change). Social conformity was also the strongest (β = 0.43) of two significant multiple regression predictors out of 12 psychological variables. Notably, social conformity was not as strong a predictor of willingness to engage in CNM, illustrating the difference between attitudes toward and interest in participating in CNM. Social dominance orientation has been explored in relation to attitudes toward CNM in one study [76]. Separate multiple regression analyses were conducted for each of two social dominance scales for five CNM Apprehension factors (consisting of a series of negative beliefs about CNM rated on a “worried” scale). Anti-egalitarianism social dominance accounted for significant and large amounts of variance in CNM moral belief violations (18%), same-sex intimacy concerns (10%), and reputational damage beliefs (6%). Hierarchy social dominance accounted for significant but smaller amounts of variance in CNM moral belief violations (9%), same-sex intimacy concerns (5%), and reputational damage (4%). Both social dominance domains were significant predictors for CNM Apprehension regarding relationship conflict and sexual health risk, but both accounted for very small amounts of variance (<3%).

Arguably, moral decision-making philosophy may be related tangentially to authoritarianism and social dominance. Cunningham et al. [76] also found that a morality decision-making style based on authority or group hierarchy (e.g., respect for authority, valuing traditions) was a consistent predictor of all five of the CNM Apprehension scales, above and beyond personality traits, accounting for between 4% and 47% of the variance in CNM Apprehension ratings. Further, a moral foundation or decision-making belief system related to ingrouping or loyalty to one’s group (e.g., love for country, betraying one’s group) was predictive of all five CNM Apprehension scores, too (accounting for between 2% and 15% of the variance, after controlling for personality traits). These morality findings are consistent with what would be predicted based on authoritarianism and social dominance theories.

Other psychological variables that reflect authoritarianism and social dominance predict attitudes toward CNM. Cunningham et al. [76] investigated a series of moral foundations and beliefs as predictors of CNM apprehension beliefs after controlling for personality traits. Aside from the (arguably) authoritarian-relevant morality, they found purity- or disgust-related moral beliefs (e.g., whether something is indecent or distasteful) were a consistent predictor of CNM Apprehension. Disgust and purity are known to co-vary with authoritarianism, and this relationship can be interpreted as supporting the supposition that authoritarians are sensitive to dangers in the world while purity and disgust are indicators of (non)dangerous things (e.g., bad smell means eggs are rotten, do not eat them [89]).

Further, Cardaso, Pascoal, and Rosa [56] reported a heterosexism instrument as moderately strongly related to polyamory attitudes such that the more rejecting of heterosexism (e.g., disagreeing with ideas like same-sex marriage undermines societal foundations), the more favorable participants were toward polyamory. Heterosexism, as a hierarchical belief system, may reflect a social dominance orientation.

In short, there is some emerging evidence that endorsing a more authoritarian ideological system may predict negative attitudes toward CNM.

3.2.2. Personality Traits

Personality psychology has identified five superordinate traits, called the Big 5, that are theorized to work through authoritarianism and social dominance to influence person perception [84]. Moors et al. [80] found openness and conscientiousness of the Big 5 personality dimensions were the only significant multiple regression predictors of Moors et al.’s [49] Attitudes toward CNM instrument. Only openness was correlated to any extent (r = 0.30) at a bivariate level, though. However, this attitude instrument conflates four self-referent CNM attitude items (i.e., how I feel about monogamy related to myself) with only two other referent CNM attitude items. Cunningham et al. [76] also found that the openness personality trait was predictive of their participants’ overall scores on their comprehensive CNM Apprehension scale, which is also a self-referent scale (i.e., apprehension about what would happen if I participated in CNM). Skakoon-Sparling et al. [71] found no correlation between extroversion and conscientiousness with their CNM attitudes instrument; they did not calculate correlations for the other three personality traits.

3.2.3. Sociosexuality and Erotophobia–Erotophilia

Social perceivers’ individual differences related to sexuality are of potential relevance to perceptions of sexual minorities such as CNM practitioners. In particular, sociosexuality would seem to be relevant to attitudes toward CNM. Sociosexual orientation is a propensity toward casual sexuality. Sociosexuality involves motivational, attitudinal, and behavioral components [90]. Erotophobia-erotophilia, an approach–avoidance response to sexual stimuli, is a learned disposition that may be particularly relevant to attitudes toward those who engage in various sexual practices [91], such as those who practice polyamory or other types of CNM. Balzarini and colleagues [92] found that monogamous individuals generally differ from individuals with a CNM identity on sociosexual orientation and erotophobia–erotophilia such that the latter were more sociosexually unrestricted and more erotophilic than the former.

With regard to attitudes toward people who practice CNM, Cohen and Wilson [47] and Cohen [93] reported a correlation of 0.34 between sociosexuality and their CNM Attitude scale. Ka et al. [50] reported a correlation of 0.33 of sociosexual behavior (i.e., not the entire scale) and the Moors et al. [49] Attitudes toward CNM scale. Further, sociosexual behavior alone, as well as the interaction of sociosexual behavior with moderator variables, accounted for 25% of the variance in CNM attitudes in multiple regression analyses [50].

Johnson et al. [33] found that erotophobia–erotophilia correlated 0.57 with their Attitudes towards Polyamory scale. Some other sexuality-related variables were related to the Attitude towards Polyamory scale [33] at a bivariate level, including sexual sensation-seeking (r = 0.33), need for sex (r = 0.17), and sexual risk-taking (r = 0.17). Based on this limited literature, it appears that sexual dispositions can be predictive of CNM attitudes, with more sexual liberalism predicting positive CNM attitudes.

3.2.4. Attachment and Relationship Styles

Another approach to studying attitudes toward CNM involves attachment styles or the ways in which the individual approaches human relationships. Based in parent–child emotional attachment to caregivers, attachment style theory is a biologically based system that carries over to adult romantic pair bonds. Sexuality is thought to be implicated in adult attachment orientations, which have an important influence on subsequent romantic love relationships. Monogamy, within this framework, is a single pair bond that is theorized to be evolutionarily adaptive. Unrestricted sexual behavior has been linked with an avoidant attachment style [94]. Attachment theory is relevant when considering participation in CNM or willingness to engage in CNM as these implicate the self in CNM [1]. Theoretically, a perceiver’s attachment style may be less relevant to judgments about others who engage in CNM. Nevertheless, some researchers have investigated the relationship between romantic attachment style and CNM attitudes.

Moors, Selterman, and Conley [80] investigated avoidant and anxious attachment styles and attitudes and found that both styles correlated weakly (r = −0.20 and 0.11) with Moors et al.’s [49] Attitudes toward CNM scale; neither was a significant multiple regression predictor of the attitude scale when the Big 5 personality traits were included in the prediction equation. However, when excluding personality traits from the prediction equation, both avoidant and anxiety attachment did predict CNM attitudes significantly, accounting for 7% of the variance in attitudes. Ka et al. [50] used the same CNM attitude-dependent measure and found weak correlations with avoidant and anxious attachment styles (rs = 0.02 and 0.18). In regression analysis, neither predicted attitudes on their own, but avoidant attachment style interacted with sociosexual orientation to predict CNM attitudes. This interaction was such that when the avoidant attachment was high, sociosexual behavior had no relationship to CNM attitudes. However, when participants were average or low regarding avoidant attachment style, sociosexual behavior predicted CNM attitudes. In short, classic attachment styles are not overly predictive of the Moors et al. [49] CNM attitudes instrument.

Flicker and Sancier-Barbosa [57] investigated the predictiveness of love styles [95] in relation to Johnson et al.’s [33] Attitudes towards Polyamory scale. They found that most of the love styles had very weak relationships to attitudes (rs < 0.13) with the exception of the pragma love style (i.e., described as practical love; some call this “the checklist love style” because it is rationally based), which was correlated at 0.33. Those who endorsed pragmatic love were less favorable toward polyamory. Furthermore, pragmatic love emerged as a significant predictor of polyamory attitudes in a series of multiple regression analyses; it accounted for about 4% of polyamory attitudes. Not exactly a love style, but a relevant construct, Johnson et al. found that emotional jealousy was slightly related to polyamory attitudes (r_{two samples} = 0.22 and 0.35; the more jealous at the thought of a partner with someone else, the less positive toward polyamory). Skakoon-Sparling et al. [71] also found jealousy and, to a lesser extent, empathy predictive of their attitudes toward CNM scale.

Another relationship-related cognitive style is zero-sum thinking. Cunningham et al. [76] investigated zero-sum romantic beliefs as predictors of CNM Apprehension. Simply put, zero-sum romantic thinking involves endorsement of the idea that love is finite; essentially, one partner receives 100% of the love available, and two partners would involve splitting that 100% (e.g., 75/25, 50/50). This zero-sum bias can apply even if desirable resources are unlimited (love can be thought of as unlimited [54,96]). Of all the variables investigated in this study, zero-sum romantic beliefs were the most powerful, accounting for 21% to 33% of the variance in CNM apprehension responses (after controlling for personality traits). In a scenario study depicting either monogamous or CNM relationships, Burleigh et al. [54] also found that endorsement of zero-sum romantic beliefs resulted in reduced evaluative judgments of the CNM couple but more favorable ratings (e.g., ethical, kind, not selfish) of the monogamous couple.

If we have a valued, limited resource, we want it all for ourselves. In this way, zero-sum thinking, pragmatic love styles, and jealousy as predictors of CNM attitudes are consistent with authoritarianism and social dominance perspectives on CNM. That is, CNM is a danger to or threatens the 100% devotion my partner should have for me; CNM prevents me from receiving all of my partner’s love, which I deserve because I am #1.

3.3. Theoretical Integration of Predictors of CNM Attitudes

In sum, the literature regarding the prediction of attitudes toward CNM relationships or practitioners can be interpreted consistently within the Dual-Processing Motivational Model, whereby two main motivational constructs underlying prejudice are authoritarianism and social dominance. While authoritarianism was originally described as a personality trait, Duckitt and Sibley define authoritarianism [RWA] and social dominance [SD] as “…two broad motivationally (or value) based social attitude or ideological dimensions: RWA is defined as a threat-driven attitudinal expression of the values or motivational goals of collective security, control, stability, and order. SD is defined as a competition-driven attitudinal expression of the values or motivational goals of power, dominance, and superiority” ([83], p. 190). Many of the variables investigated in the CNM attitude literature are consistent with these two motivational goals, particularly with authoritarianism. For example, the practical love style or zero-sum thinking is consistent with the preferred concrete thinking style of authoritarians; the original authoritarianism was theorized to reject creative, open-minded thinking (called anti-intraception [97]). Many of the predictors of attitudes toward CNM relationships and individuals—such as sexual orientation, religion, political orientation, erotophobia–erotophilia, sociosexual orientation, openness, and moral decision-making—can be construed as reflecting conventionalism, one of the cornerstones of authoritarianism. CNM relationships and individuals are viewed as a threat to tradition and the status quo. The sine qua non of society is the couple, often synonymous with “the family”, which is often based on a marriage of two people. Cohabiting couples are viewed favorably, but marriage is generally rated as better [98], while single people are often stigmatized for not being in a romantic relationship [99]. Those who reject the couple archetype by being involved in a CNM relationship may be viewed as attempting to topple this relationship hierarchy and thus evoke the ire of those who endorse social dominance. However, social dominance may be more relevant in the prediction of self-related attitudes regarding CNM (e.g., willingness to engage in CNM, sociosexual attitudes) as the basis of social dominance is competitive thinking.

While theoretical explanations of psychological phenomena should be robust in relation to prediction across multiple outcome modes and research designs, the form of assessment can have an influence on the findings and consequent theoretical interpretation [35,36]. A complicating issue in assessing if CNM attitudes are (relatively) positive or negative or what predicts CNM attitudes is the different approaches to assessing CNM attitudes. For example, the prediction of specific prejudicial behavior will be enhanced when the underlying theoretical constructs correspond closely with the behavior. Conceptual definitions of CNM attitudes and the consequent measurement of CNM attitudes are critical for understanding, predicting, and changing negative behavior (or fostering desirable behavior). While speaking of another branch of attitudes, Fishman et al. [100] synopsize the issue well: “Without standardized approaches, it is difficult for the research to develop a common scientific language, compare or pool findings across studies, or develop theories that can establish causal mechanisms …” [p. 8]. A major issue with the CNM attitude literature is the different ways CNM attitudes are assessed. This inhibits our ability to draw conclusions because we are comparing apples to oranges. To address this, existing scales are discussed, and measurement practices are suggested.

4. The Measurement of Attitudes toward CNM

4.1. Existing Scales

How researchers have assessed attitudes depends on the study design. When assessing individuals in CNM specifically, such as in a scenario study, items specific to the traits of the persons/relationship were typically used. However, there is a need for scales that measure attitudes toward CNM generally. Currently, there are a handful of multi-item measures used by researchers to measure attitudes toward CNM (see Appendix B for the scales’ content). The scales developed to assess beliefs about CNM include the following:

(1) The six-item Attitudes toward CNM scale, developed by Moors et al. [49], has been used frequently in the literature. The scale does not appear to have been subject to factor analysis but does seem to have good internal consistency (alphas of 0.79 [49,76] and 0.90 [60,80]). There is a conceptual problem with this scale, given that four of the six items implicate the self in the assessment of CNM attitudes; it does not measure attitudes toward others solely.

(2) The eight-item Consensual Non-Monogamy (CNM) Attitude scale was created by Cohen and Wilson [43]; one of the eight items refers to the self in relation to CNM, but otherwise, the content assesses beliefs about monogamous and non-monogamous relationships (e.g., CNM is too complicated). The validation study [47] involved an exploratory as well as confirmatory factor analysis, and it demonstrated good internal consistency (alphas of 0.80–93; [46,48,58]).

(3) The seven-item Attitudes towards Polyamory scale was created by Johnson et al. [33]; the authors reported the results of exploratory and confirmatory factor analyses, which produced a single factor with good internal consistency (alphas 0.86–0.88). Subsequent research teams have deleted a religiosity-based item due to poor factor loading. The consequent six-item inventory has been validated independently with confirmatory factor analyses [56,74] and substantial alphas reported (0.80–0.86 [45,56,57]). Thompson, Bagley, and Moore [45] changed “polyamory” to “non-monogamy”, thus making the scale more broadly applicable. Unlike the Attitudes toward CNM scale [49] and the CNM Attitude scale [47], the Attitudes Towards Polyamory instrument’s item content does not refer to the self’s involvement in CNM, making it the strongest “attitudes toward” instrument, from a content validity perspective.

(4) CNM Apprehension [76] is a multifactor instrument that specifically assesses beliefs that would influence the perceiver in terms of entering into a CNM relationship. This instrument assesses negative beliefs, specifically, and uses a “worried” rating scale. It is not an attitudes scale, per se, but its name reflects the construct it measures. Further, strong methodology was used to identify the item content. Specifically, the issues of concern were solicited from participants. Then, 56 unique issues were created from these participant responses. With a separate sample, the 56 were reduced to 40 items using principal components analysis. Five factors were identified: (1) Relationship Conflict, which consisted of 23 items describing how CNM would result in problems in the primary relationship; (2) Moral Belief Violation, which addresses threats to family and societal traditions; (3) Reputational Damage reflects normative disapproval and consequences of one’s participation in CNM; (4) Sexual Health Risk consists of only two items, which address beliefs about CNM and STI risk; and (5) Same-Sex Intimacy, whereby items assess discomfort with CNM possibly resulting in same-sex interactions. A total CNM Apprehension score aggregate correlated extremely highly with Moors et al.’s [49] Attitudes toward CNM scale (r > 0.70). The beliefs statements could be adapted to refer to others rather than the self.

(5) The Multidimensional Measurement of Attitudes toward Consensual Non-Monogamy scale (MACS; [71]) is a 16-item, three-factor instrument. Developed from an initially large pool of items constructed via literature review, clinical experience, and expert panel review, subscales include (1) CNM as Dysfunctional, which involves seven items reflecting beliefs about the emotional underdevelopment of CNM, and (2) CNM as Immoral, reflecting moral beliefs, for example, implicating children. The four items of this scale are reminiscent of the CNM Apprehension Moral Belief Violation scale [76]. (3) CNM as Healthy and Satisfying reflects positive beliefs about CNM.

(6) A final dependent measure worth mentioning in this list of instruments is the CNM person-specific assessment created by Grunt-Mejer and Campbell [61]. In assessing vignettes, they created person-perception scales: (1) relationship satisfaction, with 15 items; (2) cognitive or competence abilities, consisting of six items; and (3) morality, also six items. They replicated the research [62] and modified some items, thereby reducing the scales to eight, five, and five items, respectively. These authors provided item content along with descriptive statistics for each item and alpha coefficients for the scales (i.e., 0.92–0.94, 0.84–0.85, and 0.80–0.82, respectively). This is a targeted person-perception instrument and does not speak to CNM specifically.

4.2. Critique and Use Recommendations

Due to the use of the vague term “CNM attitudes”, the construct being measured may be obscured. There is a very important distinction between attitudes toward others who engage in CNM and attitudes toward the self’s involvement in CNM. The conflation of the self (four of six items) and others (two of six items) in Moors et al.’s [49] Attitudes toward CNM makes this instrument problematic as a measure of attitudes toward CNM as it is more akin to one’s own willingness to engage in CNM. Cohen and Wilson’s [47] CNM Attitude scale suffers from this issue as well, although only one of eight items is self-referent (i.e., “I can see myself entering into a non-monogamous relationship”).

The advantage of the first three CNM attitude scales listed above is that they have been used in more than one study and, sometimes, with researchers independently of the scale’s creators. The latter two scales [33,47] were developed using strong, comprehensive test construction techniques.

If a researcher’s goal is to measure attitudes toward CNM in relation to the rater’s participation in CNM, the CNM Apprehension scale is well-designed, has good psychometric properties, and allows the researcher to be able to select specific scales. The authors have also used a total CNM Apprehension score [76]. The disadvantage is that the CNM Apprehension scale has a large number of items and has not been used in much research compared to the Attitudes toward CNM scale [49], which is shorter and has been used in several studies. However, the Attitudes toward CNM scale items are a mix of attitudes toward CNM, generally along with attitudes involving the self, so the construct being measured is imprecise.

If a researcher’s goal is to measure beliefs about CNM, the MACS instrument [71] shows much promise. It has three scales that can be combined into a total score. The test development was excellent. The MACS has not been used in the literature, and it involves a larger number of items than the Attitudes towards Polyamory scale [33]. The Attitudes towards Polyamory scale has only six items, is unidimensional, has been investigated independently, and the target can be changed to CNM from polyamory if desired. The CNM Attitudes scale [49] does not have quite as much face validity as the Attitudes towards Polyamory scale because of the item assessing CNM in relation to the self.

If a researcher wishes to compare attitudes toward CNM couples to other types of couples, the Grunt-Mejer and colleagues [61,62] instrument is a good choice. Because the items are targeted at the couple rather than at CNM, per se, using this scale as a dependent measure means that assessments of people who practice CNM could be compared to other couples (e.g., BDSM practitioners, same-sex, interracial, interreligious, or other heterogamous couples). Thus far, in the literature, CNM couples seem to have been compared only to monogamous couples or couples where infidelity has occurred (although, see [72]).

In sum, the Attitudes towards Polyamory scale [33] is a short, unidimensional assessment of CNM. The Multidimensional Measurement of Attitudes toward Consensual Non-Monogamy [71] scale is very promising; the MACS is multidimensional and has been developed and assessed using excellent test construction techniques. CNM Apprehension [76] is a good measure for assessing negative beliefs about one’s own participation in CNM, but it is clearly not an “attitudes toward CNM” instrument. When assessing scenarios or vignettes, the Grunt-Mejer and Lys [62] three-domain person-perception rating scale appears to have some good psychometric properties.

5. Directions for Future Research

These scales have been used as dependent measures, yet none have produced evidence of predictive validity. That is, these scales—which are belief-based—need to demonstrate that they predict attitudes. Attitudes are overarching evaluations and are typically measured on semantic differential scales [35,36]; the correspondence of item content with regard to the belief target and the semantic differential is very important (e.g., [100]). Another measure of attitude that could be used is the feeling thermometer (e.g., [72]) directed at CNM practitioners as well as CNM as a concept. How these belief-based instruments predict general attitudes needs to be established. While theoretically measuring different aspects of attitudes, some preliminary research has investigated how these explicit measures overlap with the implicit attitude test (e.g., [45]). Normative beliefs have often failed to be assessed (CNM Apprehension’s Reputational Damage subscale [76] is the exception, although the self is the attitude target).

The relationships between these instruments and actual behavior have not been investigated. Researchers need to demonstrate how well these instruments predict behavior. Social distance instruments are intermediate scales between attitudes and behavior (e.g., [55]). Researchers should investigate how the belief-based scales relate to intentions (e.g., likelihood of hiring a CNM childcare worker, willingness to rent a property to a CNM practitioner) as well as actual behavior (e.g., an in-lab assessment of how close a participant sits to a researcher confederate identified as a CNM practitioner; participant endorsement of a faux pro- or anti-CNM petition). Intentions are often used as proxy measures for behavior. Past behavior in relation to CNM targets has also not been assessed; generally, past behavior is often a good predictor of future behavior.

6. Conclusions

Assessment and understanding of attitudes toward CNM are in their infancy. While great strides have been made in the development of instruments to assess attitudes toward people who practice CNM, the literature is somewhat muddled because of different types of research design, dependent measures that conflate beliefs involving the self and others, and lack of theoretical framing of research questions. Regardless, some conclusions can be made with certainty; on average, attitudes tend to hover around neutral. Overall, there are no gender differences in attitudes toward CNM. There are demographic and psychological variables that are generally predictive of attitudes toward CNM. These variables tend to be consistent with a conventional ideology (e.g., political conservatism, social conformity), predicting somewhat negative CNM attitudes. What is lacking in the CNM attitude literature is attention to and application of general attitude theory as well as adherence to psychological measurement standards. Future research needs to ground CNM prejudice investigations in established attitude theories such as the Theory of Reasoned Action [35,36] or the Dual-Processing Motivational Model of Prejudice [83,84,85]. This will help direct assessments of CNM attitudes systematically as well as foster a greater understanding of underlying causes and the behavioral outcome implications of CNM attitudes. Once CNM attitudes are framed within theory and tested systematically, practitioners, educators, and researchers can address beliefs and attitudes held by social perceivers via interventions designed to change these components with the ultimate goal of fostering positive evaluations and reducing prejudice, discrimination, and stigma.