A study is planned to check stool occult blood positivity using hemoccult test among a group of paicipants aged 50 - 75 years. The test is repeated if result is positive. No repeating if the test is negative. What is the effect on sensitivity and specificity?: (A) Sensitivity increases specificity decreases, (B) Sensitivity decreases specificity increases, (C) Sensitivity unchanged specificity increases, (D) Sensitivity increases specificity unchanged
Answer is B. SCREENING TESTS IN One test (after +ve result) after other Both tests applied together COMBINED SERIES PARALLEL SENSITIVITY Decreases Increases SPECIFICITY Increases Decreases PPV Increases Decreases NPV Decreases Increases