The ICPHREG procedure fits proportional hazards regression model to interval-censored data, including left-censored data and right-censored data as special cases. You can select a piecewise constant function as the baseline hazard, or you can model the cumulative baseline hazard function by cubic splines (Royston and Parmar, 2002). PROC ICPHREG estimates the regression coefficients and the hazard parameters by maximizing the full likelihood function. For more information about PROC ICPHREG, see Chapter 51: The ICPHREG Procedure.