Question 3.)
Assume that there is a diagnostic test for a certain disease. The test is applied to a population
and the results are given in the below chart. Please note that the values on the chart show the
number of patients with the given specifications.
Patient with disease
Patient with no disease
Positive test result
44
10
Negative teset result
26
86
a.) What is the incidence of the disease in the population?
The incidence is the proportion of patients with disease in the entire population.
Patien with disease = 44 + 26 = 70
Population = 44 + 26 + 10 + 86 = 166
Incidence =
70
166
= 0.421 = %42.1
b.) What is the probability of the test being negative for a random person from the population?
The probability of the test being negative for a random person is the ratio of all negative results on
population.
Total number of negative test results = 86 + 26 = 112
Population = 44 + 26 + 10 + 86 = 166
The probability of test being negative =
112
166
= 0.674 = %67.4
c.) What is the probability of the test being negative for a person if it is given that he/she has the
disease?
The probability of the test being negative if the patient has disease is the ratio of true negative results
on all the results of patients with disease.
True negative test results = 26
All the test results of patients with disease = 26 + 44 = 70
The probability of test being negative if the patient has the disease =
26
70
= 0.371 = %37.1