Hello, I'm calculating confidence intervals for an incidence rate and came across this issue. I have 8 events with a total follow-up time (days/years/log) of 69166/189.37/5.25. By hand, I would calculate the confidence intervals by using the equations (Poisson distribution, alpha=0.5): ll = (CINV(0.05/2,2*n)/2)/(fu/365.25);
ul = (CINV((1-0.05/2),2*(n+1))/2)/(fu/365.25); Being n=8 and fu=69166. I get 18.23 and 83.24 x10^-3 for the lower and upper confidence intervals. Why don't I get the same result if I try to calculate these intervals by using proc genmod? PROC GENMOD DATA = ir;
MODEL n = /dist=P OFFSET= lfu_year;
ESTIMATE "intercept" intercept 1;
RUN; Assuming ir is a dataset with 1 row and 2 variables (n=8 and lfu_year=5.244)?. I get 21.1 and 84.5 x10^-3 for the lower and upper confidence intervals. Also, could you explain to me why we set the estimate "Intercept" at 1? Thanks in advance,
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