Like yourself, many others have come out with the same response: LR(-) matters
and LR (+) alone is not enough for understanding a diagnostic test's
applicability for a given disease. This discussion has been enlightening.
Thanks to every one.
Sachin Dave.
"Montori, Victor M., M.D." wrote:
> Wait a minute
> You loose info if you don't calculate LR(-)
> For A about 0.6, for B about 0.2 and for C 0
> The intuition is to choose C as a screening test. If it is negative (LR-)
> you rule out disease. To rule in disease all would be equally useful (LR+)
> as demonstrated.
> You do not loose info if you are aware of all LRs for the test. I definitely
> like LRs more when one deals with non-dichotomous results. That is when they
> really shine!
> Victor
>
> -----Original Message-----
> From: Sachin Dave [mailto:[log in to unmask]]
> Sent: Monday, September 20, 1999 7:33 AM
> To: Atle Klovning
> Cc: [log in to unmask]
> Subject: Re: Likelihood ratios (and a CAUTION)
>
> Do we really loose any information when it comes to applicability of LR's
> to a clinical problem ?
> Let us say for example there are 3 tests A, B, C with sens. and spec. as
> outlined by you for a given disease. My bottom line would be what is the
> post-test probability of that disease given a positive result of test A or
> B or C. Does post-test probability change ? Would clinician care for the
> sens. or specificity of the test A or B or C ? What he wants to know is
> how sure he can be about a disease given a positive test result.
>
> Sachin Dave, MD.
>
> Atle Klovning wrote:
>
> > The holy LR is a vast step forwars in understanding tests- BUT when
> > combining sens and spec into ONE measure- we lose information. E.g. at
> > times having a test with high specificity is very important, whereas at
> > other times high sensitivity is the thing you want.
> >
> > Also, and quite disheartening:
> >
> > A sens 40% and spec 98% => LR+ =20 and
> > B sens 80% and spec 96% => LR+ =20 and
> > C sens 100% and spec 95% => LR+ = 20
> >
> > A, B and C should generate very different test interpretations
> >
> > *******************************************************************
> > Atle Klovning, MD, Research Fellow,
> > Specialist in General Practice/Family Medicine
> > Div. for General Practice,
> > University of Bergen, Norway
> > (+47) 55 58 67 09
> > (+47) 55 58 67 10 (FAX)
> >
> > http://www.uib.no/isf/people/atle/
> >
> > *******************************************************************
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