<unk> of clinical trials is the partitioning of subjects and results by a factor other than the treatment given.<unk> can be used to ensure equal allocation of subgroups of participants to each experimental condition. This may be done by gender, age, or other demographic factors.<unk> can be used to control for confounding variables (variables other than those the researcher is studying), thereby making it easier for the research to detect and interpret relationships between variables. For example, if doing a study of fitness where age or gender was expected to influence the outcomes, participants could be stratified into groups by the confounding variable. A limitation of this method is that it requires knowledge of what variables need to be controlled.
Stratification 
Adaptive design 
Sampling 
Revalidation
Normalization model
Mutual standardisation
Sensitivity training
Validation 