How many studies should be included in a systematic review?

Systematic reviews have become a cornerstone of evidence-based practice in nearly every field and industry. This is because many studies have been published, and there is a need to synthesize their findings and put them into practical use. As you conduct your systematic review, you may have asked yourself, “How many studies should be included in a systematic review?”

You are not alone. As industry leaders in writing systematic reviews, one of the most frequently asked questions we encounter from those seeking our services is how many articles are needed for a systematic review.

How Many Studies Should be Included in a Systematic Review?

To cut the long story short, the role of a systematic review is to synthesize all the available literature to answer a focused research question. This is what Cochrane says in their definition of a systematic review in their handbook. Yes, the keyword here is ALL.

The main implication of the definition of a systematic review is that there is no definitive answer to the question of the number of studies needed for a systematic review. If there are 100 articles that meet your pre-specified criteria, then you must use all one hundred articles. If there are only five, then your systematic review will only have five.

This is why conducting a systematic review takes a lot of time, especially if there is a large number of articles to synthesize. However, based on my experience of more than 12 years as a systematic reviewer, I can confidently say that most systematic reviews tend to synthesize between 6 and 20 articles.

Reasons Why Most Systematic Reviews Use Between 6 and 20 Articles

There are several reasons why most systematic reviews fall within the category of 6-20 studies.

First, if there are numerous articles that meet your eligibility criteria, it is highly likely that other systematic reviews have already been conducted. Since most researchers aim for originality in their work, no one would want to repeat what others have already done.

Second, systematic reviews tend to focus on areas with limited research, resulting in only a few eligible studies.

Third, searching a small number of databases can also yield a small number of articles.

Finally, I have encountered scenarios where researchers were too lazy and decided to include a predetermined number of articles in their review.

In summary, when conducting a systematic review, questions like “how many articles for a systematic review,” “how many articles needed for a systematic review,” and “how many studies for a systematic review” are common. Now you know that the role or purpose of a systematic review is to synthesize all available evidence. If not, that is not an ideal systematic review, but rather something like a rapid review.

At SystematicReviewPro, we understand that conducting a systematic review can be extremely hectic. It requires a significant time investment to search for all the available evidence eligible to answer a specified research question. Not to mention the screening process, data extraction, data synthesis, and report writing. Our community of PhD scholars can help you conduct the entire systematic review process, from determining a topic to conducting database searches and screening, to writing the report. Try us today for optimal results for your systematic review.