Question

You will be assessing the appropriateness of a new screening test for Disease X. Assume a population of 1000 people of whom 100 have Disease X and 900 do not have Disease X to answer questions a through i using the following 2x2 table:

	Disease	No Disease
Positive screen	80	100
Negative screen	20	800

1.      Calculate the sensitivity.

2.      Interpret your sensitivity calculation and the implications for potential use of this screening test.

3.       Calculate the specificity.

4.      Interpret your specificity calculation and the implications for potential use of this screening test.

5.       Calculate the predictive value of a positive test?

6.       Interpret the above calculation and the implications for potential use of this screening test.

7.      Calculate the predictive value of a negative test?

8.      Interpret the above calculation and the implications for potential use of this screening test.

9.        What is your assessment of the use of this screening test for Disease X in practice? Should it be used? Why or why not?

Answer 1

1. Sensitivity = 8/10

2. the result comes out to be that 80% of people, it shows that the probability of people having the disease amongst the disease. Sensitivity is two-thirds, so the test is able to detect two-thirds of the people with the disease. The test misses one-third of the people who have a disease.

3. Specificity = 8/9

4. the result comes out to be that 8/9 people, which is a fraction of those that will not have the disease.

5. A/(A+B)*100 = 80/(80+100)*100 = 44.44%

6. this means that of the people that had a positive test only 44.44% actually have the disease.

7. D/(D+C) *100 = 97.56%

8. for the people that tested negative, 97.56% does not have the disease.

9. all tests have advantages and disadvantages, such that no test is perfect. There is no free lunch in disease screening and early detection.