Programming the statistical procedures from SAS

Relative risk per a unit decrease instead of increase?

Reply
New Contributor Gen
New Contributor
Posts: 2

Relative risk per a unit decrease instead of increase?

Hi,

I obtained relative risk (RR) using PROC PHREG for a continuous predictor.  By default, the RR was calculated for a unit INCREASE of the predictor, However, what I want to obtain is the ratio per a unit DECREASE. In other words, SAS calculates  "(risk in a higher level) / (risk in a lower level)" but I want to make SAS to calculated "(risk in a lower level) / (risk in a higher level)." If you know how to obtain relative risk or odds ratio per a unit decrease of a continuous predictor with a command other than PROC PHREG (i.e., PROC REG, PROC LOGISTICS, etc...), please share your knowledge.

Following are the codes that I used.

proc phreg data=please;

  model time*event(0)=continuous_predictor;

run;

Thanks!

Grand Advisor
Posts: 16,933

Re: Relative risk per a unit decrease instead of increase?

Try HazardRatio statement with unit = -1.

New Contributor Gen
New Contributor
Posts: 2

Re: Relative risk per a unit decrease instead of increase?

Thank you for your comment, Reeza. Would you specify what you mentioned above? 

Grand Advisor
Posts: 16,933

Re: Relative risk per a unit decrease instead of increase?

Hmm...I thought the following would work, but I guess not since unit only accepts positive values. 

Not sure Smiley Sad

proc phreg data=please;

  model time*event(0)=continuous_predictor;

hazardratio continuous_predictor/unit=-1;

run;

SAS Employee
Posts: 187

Re: Relative risk per a unit decrease instead of increase?

PROC LOGISTIC will also report the odds ratio for a unit increase in the continuous predictor.  To get the reciprocal of that odds ratio, you would have to model the other level of the binary response.  For example, if your response levels are coded 0 and 1 and you model the probability of 0:

model y(event="0")=x;

then modeling the probability of 1 will give an odds ratio that is the reciprocal of the above:

model y(event="1")=x;

Ask a Question
Discussion stats
  • 4 replies
  • 243 views
  • 0 likes
  • 3 in conversation