Introduction to Epidemiology 6th Edition by Ray M Merrill

Exercise 2

A screening test for a newly discovered disease is being evaluated. In order to determine the effectiveness of the new test, it was administered to 880 workers, and 120 of the individuals diagnosed with the disease tested positive. A negative test finding occurred in 50 people who had the disease. A total of 40 persons not diseased tested positive for it. Construct a 2 × 2 table, similar to the one in Table 1, and calculate the following:

a. Prevalence of the disease

b. Sensitivity

c. Specificity

d. Predictive value positive

e. Predictive value negative

f. Likelihood ratio positive

g. Likelihood ratio negative

h. Overall accuracy

Table 1 True Disease Status According to Possible Test Results

True Disease Status
Test Result	Present	Not Present
Positive	TP	FP
Negative	FN	TN
	TP + FN	FP + TN

Step 1 of 9

While evaluating a screening or diagnostic test, the following results may be obtained

True positives (TP) – indicate that the person has the disease when, in fact, they do.

False positives (FP) – indicate that the person has the disease when they do not have it

False negatives (FN) – indicate a person does not have the disease when, in fact, they do

True negatives (TN) – indicate a person not having the disease when, they do not