Is it normal for a PhD thesis' methods chapter to show a high similarity index on iThenticate?

Question

I'm just about to submit my thesis to the library and after putting my entire materials and methods chapter to iThenticate, I found quite a bit of overlap with previously published papers from my lab (i.e. 20-27%) Sure, there were many false positives of common buffer and reagent names. On the other hand, there were sentences with technical jargon that were not easy to paraphrase (think: LC-MS/MS set up) or things I've grown accustomed to saying in lab after four years ("I then used this assay to measure concentration" or the list of set procedures used for raising cells). There's only so many ways to say certain things and while writing a thesis, one might not have a chance to see all these similarities until the end. My two supervising profs and assessors didn't flag these issues as well.

I guess my question is, how worried should I be that some sentences of my Materials chapter are very similar to those found in published literature? If I've completed my defense and can't change my thesis (per university rules), but what should I do if I feel really bad about this?

Answer 1

In some fields, methodology is pretty standardized. Gather some data, do some statistical analysis, report the results. The creativity and innovation isn't in the methodology, per se, but in the questions asked and the possible impacts of the answers.

In such a field, it would be common to see similar wording in the required methodology section. Since you are referring to a single lab, where people also discuss things like methodology, I wouldn't be at all surprised - or worried.

In some ways the "methodology" in a field like math is so standardized that papers don't need a section on it. It is just understood. In some, the methodology is itself innovative at the moment, perhaps in machine learning. But in fields like biology and the humanities where statistical evidence may be the main driver for some threads of inquiry, you can expect similar words.

Similarity doesn't imply plagiarism. You aren't misattributing ideas by using common methodology.

What you should do is relax and except the world as it is.