<prompt> A screaning test has 99 sensitivity and 99 specificity prevalence of target disease is 5 per 1000 population. The PPV of the test -10703399  <response>: Ans. is c i.e., 33 o Positive predictive value is related to sensitivity specificity and prevalenceo This relationship is represented by Bayes theorem : -PPV Sensitivity Prevalence---sensitivity x prevalence 100-spcificity 100-prevalenceX 100o One thing should be remembered that prevalence is in percentage per 100 population not per 1000. o So, in this question, prevalence 5 per 1000 0.5 per 100 or 0.5PPV 99 x 0.5---99x 0.5 100-99 100-0.5x 100 - 33.2 