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How to compute relative risk when having 0 frequency cell

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New Contributor
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How to compute relative risk when having 0 frequency cell

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;

Super User
Posts: 11,343

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

Posted in reply to GordonC_SAS

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

New Contributor
Posts: 3

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

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

Super User
Posts: 10,020

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

Posted in reply to GordonC_SAS
proc freq data=data1;
weight Count/ZERO;
tables arm*event ;
exact RELRISK;
run;
New Contributor
Posts: 3

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

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

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