Is there any reference or guideline regarding the minimum number of studies for conducting a meta-analysis?
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2$\begingroup$ No, but two studies is enough. $\endgroup$– zkurtzCommented Sep 13, 2013 at 21:13
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1$\begingroup$ Sure, mathematically two studies are enough to calculate a summary effect size. But is there any source i could reference to justify e.g. that I report individual results when there are less than seven studies but calculate a meta-analysis for seven studies or more? $\endgroup$– jokelCommented Sep 15, 2013 at 20:19
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$\begingroup$ @jokel The question is quite pertinent and needs further investigation. I came across a doctoral thesis by Ronco L. Sharon. This thesis brings out that k = 20 is sufficient for an effect-size. The detailed reference is available in the article by me- meta-analysis of sample correlations. It can be downloaded from ssrn.com or EBSCO-HOST $\endgroup$– user10619Commented May 11, 2014 at 12:05
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There's actually no minimal (or maximal) number needed for a pooled analysis (e.g. meta-analysis). I've conducted systematic reviews including one trial to over 250 trials. As long as you can analyze data from two separate sources then it is a meta-analysis. If you have a limited number of studies contributing to the meta-analysis then some analyses are not advisable (e.g. publication bias tests, meta-regressions, subgroup/ sensitivity analyses, etc.) due to low power.
Hope this helps.
Ahmed
