Statistical power analysis

  • The power calculator computes the test power based on the sample size and draw an accurate power analysis chart.

Larger sample size increases the statistical power.

  • The test power is the probability to reject the null assumption, \(H_0\), when it is not correct.
  • Power is expressed mathematically as \(1 - \beta\).
  • Researchers usually use the power of 0.8 which means the Beta level (\(\beta\)), the maximum probability of type II error, failure to reject an incorrect \(H_0\), is 0.2.
  • The commonly used significance level (\(\alpha\)), the maximum probability of type I error, is 0.05.
  • The Beta level (\(\beta\)) is usually four times as big as the significance level (\(\alpha\)), since rejecting a correct null assumption consider to be more severe than failing to reject incorrect null assumption.