## 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).

**Example:**

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

**Outcome:**

Treatment A | Treatment B | Placebo | |
---|---|---|---|

n(%) | 21(29.3) | 25(25.1) | 6(9.1) |

Difference From Placebo | 18 | 11.3 | |

p-value for difference | 0.0004 | 0.067 | |

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:

PROC FREQ DATA=adtte;

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 ! 🍉