The therapeutic intervention whose effect I need to meta-analyse has several regional variants, that amount to small-to-medium differences in how the therapy is administered to patients.
Now, there is of course a trade-off between the number of studies (data points) that are meta-analysed, and the precision of the meta-analysed summary measure. What determines whether I should
- (i) pool across these variants to cast a wider net and increase my estimate's precision (reduce CIs), versus
- (ii) carry out separate meta-analyses for each identifiable study variant, in order for the effect to be more meaningful within each variant, but at a cost of course to the precision of each of those?