Inclusion and Exclusion Criteria: A Source of Common Writing Errors in Clinical Research 

We all understand that clear communication is of paramount importance in research. That said, there are certain issues that tend to pop up in research-related writing, including the way inclusion and exclusion criteria are phrased. This isn’t just an issue of grammar—unclear criteria can obscure what was studied and create difficulties during peer review and after publication. As writers, we often miss the unclear phrasing, unneeded repetition, and imprecise usage that can make the difference between an excellent paper and one that ends up being desk rejected. Our editors frequently see this in clinical manuscripts: the criteria are scientifically sound, but the sentence describing them says something the author didn't intend.

What Are Inclusion and Exclusion Criteria? 

Inclusion and exclusion criteria are the characteristics that determine who is included in a human research study. They may include age, race, sex and other demographic information; past or current disease status; and the ability to understand the study and provide informed consent. They are vital aspects of any clinical trial, and they must clearly indicate who is being included in that trial. That said, human beings can't be criteria, although they're often described that way when authors lay out the inclusion and exclusion criteria for their studies.  

Why Phrasing Matters 

Precision, whether in terms of measurements or how research is described, is important. Descriptions of research must be written to be as clear as possible so that an article stands up to the peer review process. More importantly, other researchers need to have an unambiguous understanding of what you did and how you did it so that your work is testable and ultimately reproducible. 

Common Errors and How to Fix Them 

Here, we'll take a look at some examples of problematic phrasing and how to fix these errors. 

Participants as Criteria 

Describing study participants as criteria is one of the most common errors our editors flag. The criteria are used to determine who or what is included in a study. As such, they can't be the criteria themselves. 

Example 1: The inclusion criteria were participants who provided consent and completed the entire questionnaire. 

Better: Participants who met the inclusion criteria provided written informed consent and completed the entire questionnaire.

OR 

The inclusion criteria were provision of written informed consent and completion of the entire questionnaire. 

Example 1 illustrates the issue we described in our intro. By changing a few words, the participants' characteristics are brought front and centre as the criteria that allow them to be included in the study. 

Parallel Structure and a Common Problem with "And" 

Example 2: Exclusion criteria include hypertension, history of smoking, patients with history of DVT, and past clotting disorder diagnoses. 

Better: Exclusion criteria include hypertension, a history of DVT, a diagnosed clotting disorder, or a history of smoking. 

Example 2 is problematic for a few reasons. First, it's grammatically incorrect because the list of criteria lacked parallel structure. Second, the use of "and" means that all of the criteria must be met for a participant to be excluded from the study. It is more typical, however, that meeting a single exclusion criterion is sufficient (note that “and” can still be used if a participant truly needs to fulfill every criterion). Third, patients were once again referred to as criteria. 

Yes, the choice of "and" or "or" truly is a vital detail. Consider these examples: 

Send the email to Bob, Jeanne, and Rae. 

Send the email to Bob, Jeanne, or Rae. 

It's rather clear that in the first case, the email must be sent to all three people. In the second, it can be sent to any one of the three. Something similar applies to inclusion and exclusion criteria, as in these examples: 

Participants were excluded if they had a history of hypertension, cardiac catheterization, or myocardial infarction. 

Participants were excluded if they had a history of hypertension, cardiac catheterization, and myocardial infarction. 

As in the email example, the "or" set makes it clear that a participant is excluded if they had a history of just one of the listed conditions (they're also excluded if they meet two or all three). The "and" set is conjunctive, meaning that a participant is excluded only if they meet all three; meeting one or two isn't enough. 

Our editors often raise queries about issues like this, because it's one we can never fix silently. Only the author can know whether participants had to meet one criterion or all of them, which is precisely why a reviewer who comes across this sentence will stop and ask.Using "and" or "or" can make all the difference, so choose carefully. 

Criteria for Non-Human Studies and Systematic Reviews 

Some readers may wonder about non-human studies that use inclusion and exclusion criteria, such as systematic reviews. The information in this post is applicable to these types of studies as well. Here is a similar example for a systematic review: 

Example 3: 

Articles that met the inclusion criteria were 

• Articles written in English
• Papers published between 2010 and 2024 

Better: 

Articles that met the inclusion criteria were 

• Written in English
• Published between 2010 and 2024 

In Example 3, the improved version is no longer redundant and makes it obvious that an article’s language and publication date are the features that cause it to be included in the study. 

Getting It Right Before Review 

We hope that this helps clarify some of the most common errors we see in inclusion and exclusion criteria lists as well as the best practices for specifying the criteria so that they are as clear as possible. The most important point to keep in mind is that whoever or whatever is to be included or excluded must have certain features—that is, they must meet a set of criteria—but they are not, themselves, the criteria. 

Remember: Clearly stating your inclusion and exclusion criteria is vital when writing about clinical trials, systematic reviews, and other high-impact research. Our expert scientific editors can catch these easy-to-miss errors because they're reading your methods cold, the same the way a reviewer will.

See what a reviewer will see, before you submit. Get Scientific Editing.