IS COMPARISON OF THE PREVALENCE OF DISEASE APPROPRIATE
AS HEALTH INDICATOR BETWEEN TWO POPULATIONS?
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Appendix
(O/T), is the probability of old cases among
screened cases;
(C/T), is the probability of normal cases among
screened cases.
Mathematical Derivations
We can express the prevalence of the disease D
as follows:
where
N is the number of new cases
O is the number of old cases
T is the number of screen cases
Equation (1) can be also presented in the form
where
C is the number of individuals free from the
diseases, let T = N + O + C
If we are dividing equation (2) by 2, we obtain
where
(N/T), is the probability of new cases among
screened cases;
STOMA.EDUJ (2014) 1 (2)
is the probability of new cases among the screened
population; here, the utilization of the same protocol of
diagnose of a given disease D will lead to comparable
probabilities irrespective of the populations under
study. We know exactly what is going on as the cases will
be diagnosed during screening, and all the cases have
no idea that they have the disease before (Rational). The
question about delay may rise at this point, but it will not
affect the comparison.
is the probability of the old cases among the
screened popul ][ێ