Dear Paweł
Interesting question - I don't think its a mistake and commonly use risk
factor information "diagnostically". For example, if someone comes in
with chest pain then myocardial infarction is a higher likelihood for me
if the person is 60 rather than 20 or has had a previous infarction. In
a chronic cough or hemoptysis, I'll consider lung cancer unlikely in a
non-smoker.
So intuitively that seems reasonable, but the maths also works the same.
Post-test Odds = Pre-test Odds x Likelihood Ratio
For test this is:
Post-test Odds = Pre-test Odds x Likelihood Ratio(test)
For risk factors this is:
Post-RF Odds = Pre-RF Odds x Likelihood Ratio(Risk Factor)
I'd be interested in others comments,
Best wishes
Paul Glasziou
> Dear Colleagues,
>
> I would like to ask you about common 'mistake' people made about risk
> factors (according to J. M. Last I define risk factor as exposure of
> behavioral pattern that improves a chance of developing the diseas in
> future). Namely, we frequently identify risk factors with some kind of
> diagnostic test, i. e. collecting patient medical history. Let's say there
> is 55 years old patient with smoking history in the past. Can we add the
> absolute risk of developing bladder cancer resulting from smoking up to
> other signs/symptoms, i.e. haematuria (blood in urine) to increase overall
> probability of the disease in diagnostic process?
>
> In my honest oppinion, this is incorrect. First of all, risk factor is by
> no means a part of constelation of symptoms that define and diagnose
> bladder cancer. I assume we cannot atribute past exposure to actual disease,
> because among others we didn't established the diagnosis yet and the risk
> of the disease can be drastically different that resulting from risk factor
> alone. Secondly, risk factors are not intended to be used as diagnostic
> test, because they're used for targeting preventive interventions.
>
> Do you agree with my assumptions? What is your oppinion / practice? Can you
> recommend any further reading covering this issue?
>
> Please forgive possible inaccuraces (I am not an epidemiologist).
>
> Best regards,
>
> Pawel Kanturski, M. A.
> Medical University of Wroclaw, Poland
>
>
--
Paul Glasziou
Director, Centre for Evidence-Based Medicine,
Department of Primary Health Care,
University of Oxford www.cebm.net
ph +44-1865-227055 fax +44-1865-227036
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