Covariates are factors which have significant impacts on the primary analysis prior to the subjects being treated. Covariates adjustment should be considered in the design and analysis stages of the clinical trial. Through controlling in the design stage is the optimal resolution; randomization, stratified randomization and restricted covariant values could be used to balance the covariates between comparative treatments. During data analysis stage, analysis of covariance, stratified analysis, linear or generalized linear model can be conducted for covariate adjustment according to different types of outcome and covariate. For confirmatory clinical trial, covariates should be defined in advance in the protocol and statistical analysis plan with the main statistical model.
