05-26-2018, 06:28 AM
in a case control-study if prevalence is low OR can be used to estimate RR. For ex if OR=2, there is "two-fold risk" of developing a disease from the exposure. the problem with this is that OR overestimates RR.
OR is a/ b divided by c/ d while
RR is a/ a+b divided by c/ c+d
so OR=0.6
the risk of colon cancer in the aspirin users is 0.6, when compared to the nonusers. It is < 1, indicating a protective effect of aspirin. So aspirin reduced the risk of colon cancer by 40%=1-0.6=0.4
OR is a/ b divided by c/ d while
RR is a/ a+b divided by c/ c+d
so OR=0.6
the risk of colon cancer in the aspirin users is 0.6, when compared to the nonusers. It is < 1, indicating a protective effect of aspirin. So aspirin reduced the risk of colon cancer by 40%=1-0.6=0.4