Date: Thu, 15 Jul 2004 22:42:55 -0400 "Edmund J. Bini, M.D., M.P.H." "SPSSX(r) Discussion" "Edmund J. Bini, M.D., M.P.H." Re: Odds Ratios and Proportions To: paulandpen@optusnet.com.au <200407160229.i6G2TAk02299@mail022.syd.optusnet.com.au> text/plain; charset="us-ascii"

Thanks Paul. I understand the part about OR overestimating RR when the outcome is common. Logistic regression is often used even if the outcome is common in order to adjust for potential confounders but people have to accept odds ratios for what they are - odds ratios - and not try to convert them to a RR. Do others feel the logistic regression should not be used if the outcome is > 10%? The part I was confused about is when they asked us to convert the OR from logistic regression to a proportion. Maybe I am reading too deep into this and they just want us to abandon the use of logistic regression and just present out data unadjusted as percentages.

-----Original Message----- From: paulandpen@optusnet.com.au [mailto:paulandpen@optusnet.com.au] Sent: Thursday, July 15, 2004 10:29 PM To: Edmund J. Bini, M.D., M.P.H. Cc: SPSSX-L@LISTSERV.UGA.EDU Subject: Re: Odds Ratios and Proportions

Hi there Edmund

'However, as both the prevalence and OR increase, the error in the approximation quickly becomes unacceptable: if the baseline prevalence is 10% an OR of 4 is equivalent to a RR of 3, a discrepancy of 25%'

Regards Paul