Sensitivity

Sensitivity is a measure that quantifies the probability that, out of all those with the preclinical disease, the test will be able to identify them as positive. The equation for this measure is (number of individuals with the preclinical disease who produce a positive test)/(number of individuals with the preclinical disease.) By the 2x2 table below, the equation is (a)/(a+c).

Specificity

Specificity is a measure that quantifies the probability that, out of all those without the preclinical disease, the test will be able to identify them as negative. The equation for this measure is (number of individuals without the preclinical disease who produce a negative test)/(number of individuals without the preclinical disease.) By the 2x2 table below, the equation is (d)/(b+d).

Predictive Value Positive

Predictive Value Positive (PVP) is the component of predictive value that quantifies the proportion of true positives among all those who test positive in the screening test. The equation for this measure is (number of individuals who test positive and have the disease)/(number of individuals who test positive.) A higher PVP means the screening test is more accurate. By the the 2x2 table below, the equation is (a)/(a+b).

Predictive Value Negative

Predictive Value Negative (PVN) is a component of predictive value that quantifies the proportion of true negatives among all those who test negative in a screening test. The equation for this measure is (number of individuals who test negative and do not have the disease)/(number of individuals who test negative.) A higher PVN also means the screening test is more accurate. By the 2x2 table below, the equation is (d)/(c+d).

2x2 Table to aid Descriptions

Example Screening Data

In this example scenario, the efficacy of colonoscopies in screening for colon cancer is being studied. The data of this study is presented in the 2x2 table below.