Statistical Power

**Explain the statistical background behind power.**

This is the same question as problem #8 in the Statistics Chapter of Ace the Data Science Interview!

Power is the probability of rejecting the null hypothesis when, in fact, it is false. It is also the probability of avoiding a Type II error. A Type II error occurs when the null hypothesis is not rejected when the alternative hypothesis is correct (false negative).

This is important because we want to detect significant effects during experiments. That is, the higher the statistical power of the test, the higher the probability of detecting a genuine effect (i.e, accepting the alternative hypothesis and rejecting the null hypothesis). A minimum sample size can be calculated for any given level of power - for example, say a power level of 0.8.

An analysis of the statistical power of a test is usually performed with respect to the test's level of significance (α) and effect size (.ie., the magnitude of the results).