Re: MSTS Risk
From: art fougner, md (evsono@pipeline.com)
Wed Feb 14 07:24:58 2001
maybe we need to get a professional odds maker from las vegas to give us
the skinny on this?
art
At Tue, 13 Feb 2001, Terry J DuBose wrote:
>
>Wayne, the Web page I pointed to earlier discussed the fact that the Odds
>Ratio is a bit counter intuitive... or a bit odd, as you put it. Check
>it out:
>http://www.jr2.ox.ac.uk/Bandolier/band25/b25-6.html
>
>--
>Terry J DuBose
>Little Rock, AR 72205
>
>On Tue, 13 Feb 2001 20:18:36 -0600 Wayne.Persutte@UCHSC.edu writes:
>> 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
>
--
art fougner, md
A series of 1000 cases begins with but a single anecdote.
