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Writing a Systematic Review Part II:
Identifying literature—Inclusion and Exclusion Criteria

Release Date: August 7, 2017
Category: Scientific Writing
Author: Katherine S., Ph.D., E.L.S.

In our last article, we discussed how to define your aim for the systematic review. Do you remember your aim?

I want to see if treatment P improves disease-free survival and the ability to perform tasks R and S compared with placebo in patients with condition X, and I’ll be using data from randomized controlled trials.

Great. Now it’s time to come up with the inclusion and exclusion criteria for the literature.

My what?

Your inclusion and exclusion criteria are a list of parameters or factors that you use to decide whether you should include a paper in your analysis. It is best to come up with these criteria at the same time as your aim to make sure the results aren’t biased. Sometimes, the criteria need to be changed once you see the number and type of articles that address your aim. However, it is best to define them before you see your search results. You can also build some of the criteria into your search terms, which will reduce the number of articles you get back.

What kind of things do I put in inclusion and exclusion criteria?

There are two types of inclusion criteria: those relating to publication details and those relating to experimental design. Publication criteria can include things like the date of publication, the language in which the article was published, whether the article was peer-reviewed, and whether to include multiple publications on the same study population. Experimental design criteria can include factors such as randomization, level of blinding (e.g., single blind, double blind, blinded assessors), prospective or retrospective studies, enrollment criteria, number of enrolled subjects, follow-up time, and acceptable outcome measures.

All of these parameters can affect your data analysis and the strength of your conclusions. You should also have a solid rationale for selecting these criteria. For example, let’s say you decide to only include papers published after 1980. If the FDA approved a device that had higher diagnostic sensitivity for condition X in 1979, that would be a good inclusion criterion. If you don’t feel like reading a paper published before you were born, that would be a bad inclusion criterion.

Okay. Let’s say that I want articles published after 1990 because data on treatment P was first published in 1990. I want articles published in peer-reviewed journals in English. I only want to include one publication per study population. I want prospective randomized control trials that must have at least 100 patients enrolled because that is minimum number of patients needed to observe a statistical difference with sufficient power. They must also have at least 5 years of follow-up because that is the minimum time to observe disease-free survival.

Those are good inclusion criteria. Now you will need to conduct your search. We’ll get into that in our next article, “Writing a Systematic Review Part III: Identifying literature—Designing a Search .”

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