topic Re: How to compute relative risk when having 0 frequency cell in SAS Programming

How to compute relative risk when having 0 frequency cell

GordonC_SAS — Fri, 14 Jul 2017 21:46:32 GMT

I have two binary variables: treatment arm (arm 1, arm 2) and event (Yes, No) for each participant. I transformed my participant-level data into a long format summary data (so now I have 3 variables: count, arm and event). My goal is to compute the relative risk of event in arm 1 comparing to arm 2, and the exact confidence interval. The problem is the frequency of the event in arm 2 is 0 (no one had event in arm 2) so I always get infinite RR. And upper bound of my confidence interal goes to infinite as well. Is there a way to avoid this problem? I learned that proc freq would add 0.5 to each frequency to ensure that the statistics is defined when there is 0 frequency table cells but I couldn't figure out the code.

Here is my code:

proc freq data=data1;
weight Count;
tables arm*event ;
exact RELRISK;
run;

Re: How to compute relative risk when having 0 frequency cell

ballardw — Fri, 14 Jul 2017 22:03:35 GMT

Can you share the cell counts you are getting in the 2x2 table?

Re: How to compute relative risk when having 0 frequency cell

Ksharp — Sat, 15 Jul 2017 11:59:37 GMT

proc freq data=data1;
weight Count/ZERO;
tables arm*event ;
exact RELRISK;
run;

Re: How to compute relative risk when having 0 frequency cell

GordonC_SAS — Mon, 17 Jul 2017 14:45:51 GMT

my cell count frequencies are:

arm 1, event = yes: 5

arm 1, event = no : 70

arm 2, event = Yes: 0

arm 2, event = No: 26

Re: How to compute relative risk when having 0 frequency cell

GordonC_SAS — Mon, 17 Jul 2017 14:51:33 GMT

I'm still getting infinite relative risk with the ZERO option.