Considering time-interaction terms using parametric survival models for interval-censoring data

Introduction: Many of the variables considered for studying in survival research are time-invariant, i.e. their values do not change over time whiletheir effects may vary over time. Therefore, the change in behavior taking place over time needs to be included in the analysis, which is done by adding time-interaction terms to the model. Method: In this research, a parametric survival model, which is able to evaluate the effect of time-dependent variables, was applied for interval-censored data in such a way that the time for invariant variables interaction was considered as time-dependent variables. Result: Using a practical example, the results indicated that parametric survival model can alter the interpretations regarding the effects of exploratory variables. Conclusion: Regarding fixed variables whose effects change over time, the researcher can incorporate their interaction effect with time, and treat them as time-dependent variables and obtain appropriate inferences.