Page 2 of 2: High Prevalence

shuvo · Credits: 4605 My Scrapbook My Reading List 11 Books

Obviously high prevalence of disease in an area affects positive predictive value. The concept of PPV is - if a test gives a positive result then what is the chance that the man is really diseased. Understandably, if the prevalence of a particular disease in an area is high its more likely that the man with the positive test result is really diseased,

eg an MT positive patient in Bangladesh or india is more likely to have tuberculosis than an MT positive Belgian in Belgium, because TB is much more prevalent in Bangladesh or India than in Belgium

Like patients with sore throat in winter is more likely to have Respiratory infection than in summer due to seasonal variation of prevalence of resp infection between winter and summer...

In maths wise-
we know, PPV= TP/TP+FP
and TP= Sensitivity* Prevalence

So when Prevalence is high, then TP is also high AND when prevalence is high then no. of FP will be low understandably, so

high prevalence>high TP and also low FP > high PPV (from the first equation)

Hope this helps....

balaji_doc · Credits: 327 My Scrapbook

hi friends,
this question can be explained with taking tuberculosis in india. since it is highly prevalent number of true positives far more exceed than false positives. also sensitivity and specificity are not the same when measured in different area adhering to same conditions. predictive value doesnot change over area. constant. not subject to variation. also negative predictive value is of more value in ruling out a disease than specificity. REFERENCE FROM NMS Biostatistics .

jabby · Credits: 3703 My Scrapbook

POSITIVE PREDICTIVE VALUE.

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