Post hoc Power Analysis: Is it an informative and meaningful analysis

Power analysis is a key component for planning prospective studies such as clinical trials. However, some journals in biomedical and psychosocial sciences ask for power analysis for data already collected and analyzed before accepting manuscripts for publications. In this report, we take a close look at such post-hoc power analysis for retrospective studies, and to see if it is informative for understanding power for detecting significant effects for results analyzed using the same data upon which the power analysis is based on. We use Monte Carlo simulation to investigate the performance of post-hoc power analysis.