How do I calculate power or sample size for meta-analyses?
In order to calculate the statistical power of a meta-analysis you need a good estimate of pooled variance of the effect size of interest and reasonable assumptions to be made about the effects of inter-study differences in exposure/conditions (heterogeneity) on both the variance and the effect estimate. All of this is non-trivial, and is best handled by a Statistician closely involved with the meta-analysis. It would be possible to add power results to all of the StatsDirect meta-analysis output, but the appropriateness of this needs further debate. Some would argue that under-powered studies should not have been performed, and will therefore question their quality for inclusion in the systematic review. If this approach is taken then pooled power is almost irrelevant.
