Probability revision in general practice: the cases of occult blood in stool in patients with indigestion, and daily smoking in patients who cough
Permanent lenke
https://hdl.handle.net/10037/12453Dato
1990Type
Journal articleTidsskriftartikkel
Peer reviewed
Forfatter
Holtedahl, Knut A.Sammendrag
Prior calculation of the sex- and age-distributed
positive predictive value (PPV) of a symptom
in relation to a disease forms the basis for probability
revision based on new information about signals
observed during the medical encounter: a symptom, a
sign, a piece of information based on the medical history, a laboratory test. Probability revision requires
estimates of sensitivity and specificity of the signal.
Probability revision following positive and negative
signals have been made for occult blood in the stool in
relation to colorectal cancer in patients presenting in
general practice with indigestion, and for daily smoking
in relation to lung cancer in general practice patients
with coughs. A positive test for occult blood in
the stool gives an approximately fivefold rise in PPV
for all age groups. For patients 50 years of age and
more PPV exceeds 10%, and for patients 70 years old
or more PPV is 18.9% for men and 25.0% for women
when the test is positive. As expected, the predicted
value decreases when the test is negative, but for old
persons the predicted value is about 1 % even when the
test is negative. Daily smoking in 60- to 69-year-old
patients with coughs increases PPV from 6.4% 10
8.5% for men, and from 0.8% to 2.0% for women.
The likelihood ratio (LR) also rises. Daily smoking is
much more common than coughing in the general
population, and daily smoking in itself therefore has a
lower PPV for lung cancer than a persistent cough.
The change in probabilities after revision is illustrated.
The results confirm that a signal conditionally independent
of signals used in the calculation of prior
probabilities is more useful than a signal that cannot
be assumed to be conditionally independent for the
patients studied.
Forlag
Springer VerlagSitering
Holtedahl, K.A. (1990). Probability revision in general practice: the cases of occult blood in stool in patients with indigestion, and daily smoking in patients who cough. Allgemeinmedizin, vol. 19: 35-38.Metadata
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