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Say you have an odds ratio which represents the ratio of outcome given a particular exposure to the outcome given no particular exposure. How can you use this ratio to make an estimate about the incidence in a population that has that known particular exposure?

For instance, say there is an OR that classifies the relationship between exposure factor E and disease D in population P. Now you have population y that has an exposure to E and you want to predict the incidence or prevalence of the disease in population Q. How can the OR for P be used to make a prediction about disease D in population Q?

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If you know prevalence of your reference group say, it is $P_1$ (for which you set the odds as 1) then the prevalence for another group is $P_1*OR$. Just remember OR$\approx\frac{P_2}{P_1}$

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  • $\begingroup$ Here is a paper, the derivation is not difficult I think. oem.bmj.com/content/55/4/272.full.pdf $\endgroup$
    – Deep North
    Jul 2 '15 at 5:35
  • $\begingroup$ I have a P1 of 49.3 per 100 people. I have an OR=114. . . Thus, if I use the equation OR≈P2/P1I get a P2 of 5620 per 100 people. How do I interpret that? $\endgroup$
    – user81225
    Jul 2 '15 at 19:30
  • $\begingroup$ There are some conditions to apply this approximation. You just use a 2x2 cross table to check how you get the odds ratio and prevalence ratio, they are not equal anyway, $\endgroup$
    – Deep North
    Jul 3 '15 at 0:10

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