I'm trying to calculate the sample size for a fictional experiment for class. The experiment is similar to measuring cholesterol until time of first CVD incident, and we would analyze it with cox regression analysis. We would have two groups of subjects that exercise and a group that does not. When I try to calculate the sample size I get high numbers, I think because I'm misunderstanding something about the variables. I wasn't told to do coxreg, so I might be mistaken about that. A paper I looked at found that rate of CVD for subjects similar to mine was 23.1 person-years. So I calculated that Eventprob=0.115 (=[23.1/1000][5 years]). Another paper I found suggested that exercise decreased rate of cvd by 23%, so I used HAZARDRATIO=0.77. I wasn't sure what to put for stddev. proc power;
coxreg
power=0.8
ntotal=.
Eventprob=0.023
HAZARDRATIO=0.77
STDDEV= 0.23;
run;
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