Table 4.
True Condition (In the Population) | ||
---|---|---|
Trial study results | Therapies are different | Therapies are not different |
Therapies are different | True positive (correct decision) | False-positive (type I error) Probability = α (same as P value) |
Therapies are not different | False-negative (type II error) Probability = β | True-negative (correct decision) |
Normally, α is 5% or 0.05 (setting a P value) and power is (1 − β), often, 0.8 or 0.9 (80% or 90% power). P value and power are used in sample size calculations.