Hypotheses Null Hypothesis (H0) Hypothesis of no difference i.e. There is no link between disease and risk factor Alternative Hypothesis (H1) Hypothesis of difference i.e. There is a link between disease and risk factor Type I error (False positive) Stating there is an association when none exits Incorrectly rejecting null hypothesis α = probability of type I error p = probability that results as or more extreme than those of the study would be observed if the null hypothesis were true General rule of thumb is that statistical significance is reached if p ≤ 0.05 Type II error (False negative) Stating there is no effect when an effect exists Incorrectly accepting null hypothesis β = probability of type II error Power (True Positive) Probability of correctly rejecting null hypothesis Power = 1 - β Power depends on Sample size Increasing sample size increases power Size of expected effect Increasing effect size increases power True Negative Probability of correctly accepting null hypothesis