A time-varying covariate (also called time-dependent covariate) is a term used in statistics, particularly in survival analysis. It reflects the phenomenon that a covariate is not necessarily constant through the whole study Time-varying covariates are included to represent time-dependent within-individual variation to predict individual responses.
In statistics, specifically in survival studies, a time-variable covariate refers to a factor that changes over time. This concept acknowledges that a covariate's value may shift throughout the research period. To account for this variation, time-dependent covariates are incorporated into models to forecast individual reactions.