Good day All: Suppose I have the data (x_data) below, and further suppose I want to calculate confidence intervals for the difference of two binomial proportions (treat A vs treat B for each trial, respectively) via proc freq as below:
proc freq data=x_data;
by trial;
tables treat*outcome /riskdiff(cl=(exact));
weight count;
exact riskdiff;
run;
proc freq data=x_data;
by trial;
tables treat*outcome /riskdiff(cl=(exact));
weight count;
exact riskdiff(method=fmscore);
run;
trial treat outcome count
1 | A | x | 56 |
1 | A | y | 14 |
1 | B | x | 48 |
1 | B | y | 32 |
2 | A | x | 9 |
2 | A | y | 1 |
2 | B | x | 3 |
2 | B | y | 7 |
3 | A | x | 10 |
3 | A | y | 0 |
3 | B | x | 0 |
3 | B | y | 20 |
I expected to get different results from the two different procedures, but I don't. The confidence intervals are exactly the same. My understanding is the former should use the Santner-Snell method ("By default, PROC FREQ uses the unstandardized risk difference as the test statistic in the confidence limit computations.") and the latter should use the Chan-Zhang method ("If you specify the RISKDIFF(METHOD=FMSCORE) option, the procedure uses the Farrington-Manning score statistic (Chan and Zhang 1999).").
What gives? BTW, I'm currently using SAS 9.4 TS Level 1M5.
Thanks