Observed Power

In this blog, I highlight a valid approach for calculating power after estimation—often called retrospective power. I provide a Shiny App that lets readers explore how the method works and how it avoids the pitfalls of “observed power” — try it out for yourself! I also link to a webpage where readers can enter any estimate, along with its standard error and degrees of freedom, to calculate the corresponding power.

Observed power (or post-hoc power) is the statistical power of the test you have performed, based on the effect size estimate from your data. Statistical power is the probability of finding a statistical difference from 0 in your test (aka a ‘significant effect’), if there is a true difference to be found.