Always consider performing a power analysis before any research study. Ideally, a statistical expert should be consulted to aid in such analysis.

Conclusions should be made based on examination of effect sizes (eg, mean differences, odds ratios, hazard ratios) and 95% confidence intervals for those effect sizes, in conjunction with P values.

Performing power analysis for any reason other than to help guide sample size decisions for a future study.

Using power analysis in order to help interpret the results of an already completed study.