Stratification

In clinical studies, stratification is often combined with randomization to balance important factors, such as disease severity or site, between groups. It improves the comparison but adds complexity to enrollment and analysis, which the statistical analysis plan has to reflect.

The division of a population into mutually exclusive and exhaustive sub-populations (called strata), which are thought to be more homogeneous, with respect to the characteristics investigated, than the total population.

FDA guidance: Design Considerations for Pivotal Clinical Investigations for Medical Devices (November 2013), Section 11, Glossary