I need help determining the correct way to compare changes in rates of two medical procedures between two groups before and after an intervention. So the data look something like this:
Before After
Proc1 Proc2 Proc1 Proc2
Group #1 21609 51815 4793 7191
Group #2 11935 67953 3808 10829
The question I want to answer is this: Is there a difference between the two groups in the change of the ratio of Proc1 to Proc2 before and after the intervention?
I was thinking of something like this (code adapted from an on-line example):
data YesNo;
length Group $ 11 ;
input Group $ Period $ Proc1 Total;
Response="Proc1"; Count=Proc1 ; output;
Response="Proc2"; Count=Total-Proc1 ; output;
datalines;
Group1 Before 21069 72884
Group1 After 4793 11984
Group2 Before 11935 79528
Group2 After 3808 14637
;
proc print noobs;
var Group Period Response Count;
run;
ods graphics on;
proc freq data =YesNo order=data;
weight Count;
tables Period*Group*response / relrisk cmh chisq plots=all;
exact eqor;
run;
ods graphics off;
Is this the correct approach? I'm not sure how to interpret the output. Any help would be greatly appreciated!
Brian
Does anyone know what eaxctly the Breslow-Day statistic is telling me when you run the code I posted? Is that just an overall comparison of the two groups or does it compare the before/after rates for each group?
Thanks in advance!
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