Statistical Significance
A measure of how likely an observed result occurred by chance. Results are conventionally significant when the p-value is below 0.05, meaning less than a 5% probability the finding is due to random variation. Statistical significance must be distinguished from clinical significance.
Technical Context
The conventional p<0.05 threshold means accepting a 5% false positive rate (Type I error). For multiple comparisons (testing many endpoints), adjusted thresholds are needed: Bonferroni correction (divide alpha by number of tests — very conservative), Holm-Bonferroni (step-down procedure), or hierarchical testing (gate-keeping, where secondary endpoints are only tested if the primary succeeds). Effect size matters alongside significance: Cohen's d (standardised mean difference) provides context: 0.2 = small, 0.5 = medium, 0.8 = large effect. For GLP-1 RA weight management trials, effect sizes for weight loss are typically very large (Cohen's d >1.0), meaning results are both statistically and clinically significant.