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Re: MSTS RiskFrom: Wayne.Persutte@UCHSC.eduTue Feb 13 19:12:03 2001
Terry, Gene, Allan, et al. Does this mean that a risk of 1 in 500 is the same as an odds ratio of 1:499?? If I am wrong, please forgive my ignorance, but I believe that reporting odds ratios in interpreting triple screen information, instead of risk (as is the more common vernacular in prenatal diagnosis) is a little odd (no pun intended). Although I have seen it before, it caught me a bit off gaurd when I saw a patient today with a 1 in 1 'risk' (as was presented to me); which made no sense. I now know that the genetic counselor intended to imply the odds ratio. Does anyone know why we use OR instead of risk? Does it simply (as Gene stated) have its roots in Bayesian analysis which is commonly used by geneticists and genetic counselors? Gene you lost me here, "Odds are different from actual risk, with one exception: when they are 1:1. If the odds are "even", or 1 to 1, you have a total of 2 different outcomes, and the risk is 1 out of 2, or 50%." First you state that the odds of 1:1 are the same as a risk of 1:1, then you seem to contradict yourself? While I think I am beginning to understand what you are saying, I am afraid you threw me a cuvreball here. Wayne -----Original Message----- From: Allen Worrall [mailto:jworrall@alaska.net] Sent: Tuesday, February 13, 2001 1:25 PM To: Multiple recipients of list ULTRASOUND Subject: Re: MSTS Risk Risk is, for example, 1 affected pregnancy in 270 pregnancies. In other words the lower or second number includes the affected pregnancy. An odds ratio is, for example, 1 affected pregnancy in x normal pregnancies. The second number does not include the affected pregnancy. Thus, to convert risk to odds, (when the risk is 1:270), reduce the second number by 1, so the odds ratio is now 1:269. So, if the risk is 1:1, I guess the odds would be 1:0, meaning there are no normal pregnancies. I am sure my explanation is simplistic.
-- Allen Worrall
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