A study is undertaken to evaluate a new serological screening test for the diagnosis of tuberculosis infection. In the study, 1000 people were randomly selected from the population and given the new diagnostic test, and positive and negative results were recorded. Each study participant also was given the gold standard diagnostic procedure to determine the true infection state of the individual. The findings are as follows: Which of the following is the positive predictive value of the screening test under study?

Question

A study is undertaken to evaluate a new serological screening test for the diagnosis of tuberculosis infection.  In the study, 1000 people were randomly selected from the population and given the new diagnostic test, and positive and negative results were recorded.  Each study participant also was given the gold standard diagnostic procedure to determine the true infection state of the individual.  The findings are as follows:  Which of the following is the positive predictive value of the screening test under study?

Quizplus · Accepted Answer

Although predictive values are not true indices of the validity of a test, these are still of prime importance to physicians. In clinical practice, patients will more often present with a positive or negative test result, rather than a disease or disease-free state; therefore, one should have sufficient knowledge about the predictive values of a test. Positive predictive value is defined as the proportion of subjects with a positive test result who actually have the disease. Negative predictive value is defined as the proportion of subjects with a negative test result who are free of disease. Consider the following 2 x 2 table: 11ec25c8_d090_f390_bc81_1b33bd2795d5_MD0003_00 Positive predictive value = TP/(TP+FP) or A/(A+B) Negative predictive value = TN/(TN+FN) or D/(C+D) In this case, the PPV is 130 / 190. (Choice A) Sensitivity and specificity are useful for assessing the validity of a test. 130/180 is the sensitivity of the test. (Choice D) 760/810 is the negative predictive value of the test. Educational objective: Know how to calculate the predictive values of a test.

A Study Is Undertaken to Evaluate a New Serological Screening