# Statistical power

## Background

- null hypothesis: there is no relationship between two measured phenomena
- often denoted H0 (read “H-nought”, "H-null", or "H-zero")

- alternative hypothesis: there is a significant relationship between the two measured phenomena
- often denoted H1

## Common Statistical Terms

SYMBOLS

- α: probability of type I error
- β: probability of type II error
- χ²: ≥ 2 percentages or proportions of categorical outcomes

TERMS

- ANOVA: compares means of ≥ 3 groups
- Confidence interval: range in which real mean expected to fall
- Negative skew: mean < median < mode
- Positive skew: mean > median > mode
- Power: probability of correctly rejecting H0
- to increase power increase sample size (most important), and/or increase expected effect size, and/or increase precision of measurement

- Standard deviation: variability from mean
- Standard error of the mean: variability between sample mean and true mean
- t test: compares means of 2 groups
- Type I error: H0 incorrectly rejected
- Type II error: H0 incorrectly accepted