Comparing withdrawal rates for a course

Which statical test should I use to compare withdrawal rates for a course for two semesters. I know I can report the means but need to know if the difference is significant.

For example:
Fall2017 10 out of 33 students withdrew
Spring2018 5 out of 66 students withdrew

Thank you in advance for your help.


TS Contributor
Alternatively, Chi² test of association (withdrawal [yes / no] crosstabulated with year [2017 / 2018]).

With kind regards



Not a robit
I would recommend looking at rate differences, in that they will provide an estimate with confidence interval:

30.3% vs. 7.6%
So, 22.7% (95% CI: 5.8%, 40.0%),

data TS;
input Exposure Outcome count;
1 1 10
1 0 23
0 1 5
0 0 61

proc freq data=ts order=data;
table exposure * outcome / riskdiff;
weight count;


TS Contributor
I'd probably also look for a CI method that preserves the nominal coverage. For a difference in two proportions, I believe the Agresti-Caffo method is a good option and if just trying to get a CI for each proportion, then the Agresti-Coull method is a good choice (but there are others with different performance characteristics).