Hi Folks:
In PROC PHREG below where METHOD is binary variable (1,0) does SAS take 1 over 0 or 0 over 1 to calculate the hazard ratio reported in the annotated output shown below?
PROC PHREG DATA=MYDATA;
MODEL DURATION*DEATH(0)=METHOD;
RUN;
Hi @Cruise,
Without a CLASS statement, METHOD is treated as a continuous variable, in which case the hazard ratio refers to an increase by one unit. For a binary variable, of course, this is equivalent to a hazard ratio of level 1 vs. level 0. Categorical explanatory variables are usually named in a CLASS statement where you can use the REF= option to specify the reference level explicitly and thus avoid any ambiguities.
Your sample output shows one of the rare cases where the "direction" (1 vs. 0 or 0 vs. 1) has no impact on the results (hazard ratio 1).
Hi @Cruise,
Without a CLASS statement, METHOD is treated as a continuous variable, in which case the hazard ratio refers to an increase by one unit. For a binary variable, of course, this is equivalent to a hazard ratio of level 1 vs. level 0. Categorical explanatory variables are usually named in a CLASS statement where you can use the REF= option to specify the reference level explicitly and thus avoid any ambiguities.
Your sample output shows one of the rare cases where the "direction" (1 vs. 0 or 0 vs. 1) has no impact on the results (hazard ratio 1).
When you switch the two levels of a dichotomous explanatory variable (used in a CLASS statement), the original hazard ratio h becomes 1/h. Similarly, the confidence limits (CL) of h are inverted: The new lower CL is 1/(old upper CL) and the new upper CL is 1/(old lower CL). Also, the sign of the parameter estimate, if positive or negative, changes (but not its absolute value, standard error, Chi-Square statistic and p-value).
However, in your example h=1 (as a consequence, the upper CL is 1/(lower CL)) and the parameter estimate is 0 so that none of the changes described above is visible.
Are you ready for the spotlight? We're accepting content ideas for SAS Innovate 2025 to be held May 6-9 in Orlando, FL. The call is open until September 25. Read more here about why you should contribute and what is in it for you!
Learn how use the CAT functions in SAS to join values from multiple variables into a single value.
Find more tutorials on the SAS Users YouTube channel.