Diana Kornbrot wrote:

yes.  we really do need both sensitivity and spec.

1.      spec lets one know about false positives and they syrely matter
clinically

    LR = true positive divided by false positive

 

2.      if one knows both spef and sens then one can estimate the effect
on performance of changing the criterion

 

depending on the costs and benefits of detection and false alarms, a
clinician mihgt wish to change the criterion

diana kornbrot

On Mon, 20 Sep 1999,
Sachin Dave wrote:

> 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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        Dr. Diana Kornbrot
        Reader in Mathematical Psychology
        Associate Dean Research, Faculty of Health & Human Sciences
        University of Hertfordshire
        College Lane, Hatfield, Hertfordshire AL10 9AB, UK
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web:    http://www.psy.herts.ac.uk/pub/D.E.Kornbrot/hmpage.html
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