Hi all, thank you for your help previously. My study currently narrowed the article list to two RCT and three open-label cohort study. However, one of the cohort study is an extension study of the other cohort study with terms of including patients from the original trial and new participants. Similar outcomes are measured, can I include it in my meta analysis as the ideal number for meta-analysis would be at least five studies.
In my view, number of studies is not a big issue if it meets your inclusion criteria. Even you can do MA with two studies. See the following RG link
https://www.researchgate.net/post/Is-there-any-minimum-number-for-studies-that-should-be-included-in-meta-analysis
I agree with Proloy Barua that the minimum number of studies in order to do a meta-analysis would be 2. How good the meta-analysis turns out depends on how exhaustive and comprehensive you had searched all the databases in order to answer your research question.
Regarding the extension study mentioned, you can include it but you should mention that it’s an extension study with additional data in your methodology.
You could include the extended cohort as it is the result of your article screening process. However, you should properly mention it in your result, as you explaining the characteristics of each included study. It won't (supposedly) affect the desired outcome nor giving another bias, as long as you are certain all the samples are subjected to similar conditions or interventions (similar starting point). If it were indeed different, you might want to try subset analysis.
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