Program for determining if aspirin is significantly better than placebo - sas

Question

I have been tasked with the following problem:
Out of a total 1,000 subjects on aspirin, 80 had heart attacks and 65 had strokes. Out of a total 2,000 subjects on placebo, 240 had heart attacks and 165 had strokes.
I am asked if there is a significant benefit for aspirin therapy for heart attacks and strokes. What is the RR for aspirin use for each of the two outcomes?
My main issue has been setting up the data lines. Here is what I have so far, but my output window doesn't look right.
Another issue is figuring out how to account for the varying sample sizes and the fact that someone might have had a heart attack AND a stroke.
DATA ODDS;
INPUT OUTCOME $ EXPOSURE $ COUNT;
DATALINES;
HeartAttack 1-Yes 80
HeartAttack 2-No 240
Stroke 1-Yes 65
Stroke 2-No 165
;
PROC FREQ DATA=ODDS;
TITLE "Odds Ratio Aspirin";
TABLES EXPOSURE*OUTCOME / CHISQ CMH;
WEIGHT COUNT;
RUN;
Edit 1:
DATA ODDS;
INPUT OUTCOME $ EXPOSURE $ COUNT;
DATALINES;
HeartAttack 1-Yes 80
HeartAttack 2-No 240
NoHeartAttack 1-Yes 920
NoHeartAttack 2-No 1760
Stroke 1-Yes 65
Stroke 2-No 165
NoStroke 1-Yes 935
NoStroke 2-No 1835
;
PROC FREQ DATA=ODDS;
TITLE "Odds Ratio Aspirin";
TABLES EXPOSURE*OUTCOME / CHISQ CMH;
WEIGHT COUNT;
RUN;

Answer 1

This is what your data and code should look like. You may need to flip the order in the TABLES statement so that the Relative Risk is calculated appropriately for your situation. I didn't bother checking that this was the case, as you can easily change if required.
DATA HeartAttack;
INPUT OUTCOME $ EXPOSURE $ COUNT;
DATALINES;
HeartAttack 1-Yes 80
HeartAttack 2-No 240
NoHeartAttack 1-Yes 920
NoHeartAttack 2-No 1760
;
PROC FREQ DATA=HeartAttack;
TITLE "Heart Attack Odds Ratio Aspirin";
TABLES EXPOSURE*OUTCOME / CHISQ CMH Relrisk;
WEIGHT COUNT;
RUN;
DATA Stroke;
INPUT OUTCOME $ EXPOSURE $ COUNT;
DATALINES;
Stroke 1-Yes 65
Stroke 2-No 165
NoStroke 1-Yes 935
NoStroke 2-No 1835
;
PROC FREQ DATA=Stroke;
TITLE "Stroke Odds Ratio Aspirin";
TABLES EXPOSURE*OUTCOME / CHISQ CMH Relrisk;
WEIGHT COUNT;
RUN;
If you have the raw data I would recommend working with that instead of creating datalines in the first place. It leaves room for errors and then you could also deal with the interaction.

Answer 2

Placebo gives you your expected distribution. We have to handle strokes and heart attacks separately because there is no data for interaction. (If there is no interaction we'd expect a small number of patients with both, but there could be a negative or masking interaction, e.g. if the heart attacks are fatal, or there could be a cumulative interaction heart attacks often preceded by strokes or vice versa). We can't answer any of those questions.
Once you've got you expected, it's simply two chi-squared tests with two bins each. Not one chi-squared test with 4 bins.
(I'll put in a plug for my book Basic Algorithms if you want to code the chi-squared significance test from the ground up, without using any loook-up tables).