How to test proportionality assumption in survival analysis using SAS

How to test proportionality assumption in survival analysis using SAS

 

There are several approaches to test proportionality assumption in survival analysis:

• Graphical Approach is to plot Log–Log survival function by researched major predictor. If the two line is parallel without cross each other, the assumption is considering confirmed.

PROC LIFETEST DATA=ONE; METHOD=KM PLOTS=(S,LLS);
     TIME SURVTIME*EVENT(0);
     STRATA RISK0;
RUN;

PROC PHREG DATA=ONE;
     MODEL SURVTIME*EVENT(0)=RISK1 AGE SEX;
    BASELINE OUT=LLSOUT LOGLOGS=LOGLOGS;
RUN;
PROC GPLOT DATA=LLSOUT;
     PLOT LOGLOGS*SURVTIME=RISK1;
RUN;

• Or, you can include an interaction term of a predictor and follow up time in the model. If this interaction term is not significant, there is no violation of assumption. For example:

PROC PHREG DATA=ONE;

MODEL SURVTIME*EVENT(0)=RISK1 TIMEX;
        TIMEX=RISK1*(LOG(SURVTIME)-LOG(average followup time));
          * someone also uses simple forms: TIMEX=RISK1*LOG(SURVTIME);
          * or even: TIMEX=RISK1*SURVTIME; (not good enough); 
     PROPORTIONALITY_TEST: TIMEX;
RUN;

• Possibly, the easiest and powerful approach after SAS 9.2 is to use ASSESS statement, for example:

ODS GRAPHICS ON;

PROC PHREG DATA=ONE;

MODEL SURVTIME*EVENT(0)=RISK1;
     ASSESS PH/resample;
RUN;

ODS GRAPHICS OFF;

 

What’s New of PROC PHREG of SAS 9.2 (pdf)