Meta-analysis should be conducted when a group of studies is sufficiently homogeneous in terms of subjects involved, interventions, and outcomes to provide a meaningful summary. However, it is often appropriate to take a broader perspective in a meta-analysis than in a single clinical trial.

When should a meta-analysis not be used?

If studies are clinically diverse then a meta-analysis may be meaningless, and genuine differences in effects may be obscured. ... A particularly important type of diversity is in the comparisons being made by the primary studies.

How do you know if you can do a meta-analysis?

If sufficient information is available to estimate the effect size of interest, then a meta-analysis is possible. ... One important point is that all studies in a meta-analysis must use essentially the same index of treatment effect. For example, we cannot combine a risk difference with a risk ratio.