# SAS Proc Freq1- Risk Difference

## SAS day 8:  Proc Freq Risk Difference

Goal :

• What is Risk Difference?
• How to interpret Risk Difference Confidence Interval.

### Background:

Risk Difference is used to compare the proportions of successes between two independent groups with respect to a binary outcome. (cancer remission).
If the outcome is continuous, we compare the difference in means instead.

Risk Difference:

where ( is the successes in group 1) ,
( is the successes in group 2).

ColiN00B / Pixabay

Example:

H0 (Null Hypotheses) :  : there is no difference in outcomes between Treatment A and Placebo.

Outcome:

Treatment ATreatment BPlacebo
n(%)21(29.3)25(25.1)6(9.1)
Difference From Placebo1811.3
p-value for difference0.00040.067
97.5% CI for Difference(9.2,35,6)(-2.2,22.3)

Interpretation:

We are 95% confident that the difference in proportion in Treatment A and Placebo is (9.2, 35.6), therefore we conclude the treatment outcome difference in success is significant.

Note: If we use the WALD option, we might get negative values for CI, which means, the difference is not significant.

SAS Code:

where (trt01pn in (1 2 ));
BY avisitn ;
TABLES trt01pn*aval / riskdiff(cl=wald) alpha=0.025;
exact riskdiff;
RUN;

data riskci;
set riskci;
col1 = put(-riskdifference*100, 4.1);
keep avisitn col1;
run;

Happy SAS Coding 😍!

Thanks very much to Renee 5, Shared the Risk Diff knowledge with me ! 🍉