Question

Given a test in which there is overlap of the test results for diseased and non-diseased individuals (e.g., normal individuals are found who have test results ranging in value from 8 to 15, and diseased individuals are found who have test results ranging in value from 12 to 25, so that in the range of values 12 to 15 there are both normal and diseased individuals), if the current cutoff value lies in the range of this overlap and you move the cutoff value toward the normal population (lower numbers in this example), the true positive numbers will _____, the true negative numbers will ____, the false positive numbers will ____, the false negative numbers will ____, the sensitivity will ____, and the specificity will ____? (Please explain each)

Answer 1

If we move the cutoff value toward the normal population, there will be large number of normal and diseased people will be tested as positive for disease. Thus, both true positive and false positive numbers will increase. Also, small  number of normal and diseased people will be tested as negative for disease. Thus, both true negative and false negative numbers will decrease.

Since true positive number increases, sensitivity will increase.

Since true negative number decreases, specificity will decrease.

If the current cutoff value lies in the range of this overlap and you move the cutoff value toward the normal population (lower numbers in this example), the true positive numbers will increase, the true negative numbers will decrease, the false positive numbers will increase, the false negative numbers will decrease, the sensitivity will increase, and the specificity will decrease.