Stratification
The process of dividing clinical trial participants into subgroups (strata) based on characteristics such as age, sex, disease severity, or baseline BMI before randomisation. Stratified randomisation ensures these important factors are evenly distributed across treatment groups.
Technical Context
Stratification variables must be: prognostic (genuinely affecting the outcome), measurable at baseline (before randomisation), and limited in number (too many strata with small blocks leads to imbalance). Typical stratification for GLP-1 RA trials: baseline HbA1c (<8.5% vs ≥8.5%), background OAD (metformin alone vs metformin + sulfonylurea), and geographic region. For weight management trials: baseline BMI (30-<35 vs 35-<40 vs ≥40) and presence of type 2 diabetes. Stratified analysis ensures treatment effect estimates are adjusted for these important baseline variables. Minimisation (a dynamic allocation method) can balance many more variables than stratified block randomisation but is more complex to implement.