STAT 301 Lecture Notes - Lecture 16: Type I And Type Ii Errors, Confidence Interval, Effect Size
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7. 3 defining statistical power: the probability of type ii error is not set by the researcher. It has to be calculated based on the design of the study: we denote the probability of type ii error as beta: Statisticians usually care about the opposite probability, the probability of not committing a type ii error. Calculating power: complicated and difficult, conceptually, we can think of the power of a hypothesis test as related to the width of a corresponding confidence interval, we will cover things that affect power. What determines power: power is determined by the sample size and effect size, as sample size increases, power increases. Suppose we compute a difference in means between a treatment group and a control group. A large difference in means would be interpreted as a large "effect" for the treatment: however, a seemingly large difference in means might not seem large if the data is highly dispersed.
