A test for disease X is found to have a test sensitivity of

A test for disease X is found to have a test sensitivity of 0.80 and a test specificity of 0.90.

Please give steps!

1. In the broad population at-large, the prevalence of disease X is 20%.   

Suppose 1000 persons drawn at random from the population undergo screening for disease X and some receive a positive test result for disease X.

Of those that receive the positive test result, what is the percentage who actually have disease X?

Solution

Sensitivity= true positives/(true positive + false negative)=0.80

Specificity=true negatives/(true negative + false positives)=0.90

Of those who receive positive actual disease = 80%