SAS Programming

DATA Step, Macro, Functions and more
BookmarkSubscribeRSS Feed
🔒 This topic is solved and locked. Need further help from the community? Please sign in and ask a new question.
Cruise
Ammonite | Level 13

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;

PROC PHREG.png

1 ACCEPTED SOLUTION

Accepted Solutions
FreelanceReinh
Jade | Level 19

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).

View solution in original post

5 REPLIES 5
FreelanceReinh
Jade | Level 19

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).

Cruise
Ammonite | Level 13
Can you please elaborate what made the case one of the rare cases where the "direction" (1 vs. 0 or 0 vs. 1) ?
FreelanceReinh
Jade | Level 19

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.

Cruise
Ammonite | Level 13
Thanks for your explanation. This helped!
Reeza
Super User
I always recommend using HazardRatio statements to interpret your HR so that you know exactly what comparisons it's making.

sas-innovate-white.png

Join us for our biggest event of the year!

Four days of inspiring keynotes, product reveals, hands-on learning opportunities, deep-dive demos, and peer-led breakouts. Don't miss out, May 6-9, in Orlando, Florida.

 

View the full agenda.

Register now!

How to Concatenate Values

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.

SAS Training: Just a Click Away

 Ready to level-up your skills? Choose your own adventure.

Browse our catalog!

Discussion stats
  • 5 replies
  • 2369 views
  • 7 likes
  • 3 in conversation