1) Which of the following term means:- amongst the subjects who receive a negative test, the proportion who are correctly diagnosed negative by the test?
2) Which of the following term means:- amongst the subjects who do NOT have the disease, the proportion correctly diagnosed negative by the test.
3) For questions 3 to 14, you must have a pen, a paper and a calculator, and draw the necessary 2 x 2 tables. A disease can be diagnosed with great certainty using CT scan. However, a diagnostic test T is used to detect a disease in population A where the disease is quite common. 1,000 patients received both test T and CT scan. 500 patients were proved to have the disease by CT scan. Of these, 400 patients were tested positive by test T. Amongst those patients who did not have the disease as shown by CT scan, 50 patients were tested positive by test T. Draw a 2 x 2 table, and answer questions 3 to 7. The prevalence of the disease (i.e. the proportion of people with the disease) is
4) The sensitivity of the test is
5) The specificity of the test is
6) The positive predictive value of the test in this population is (to the nearest %) is
7) The negative predictive value of the test in this population is
8) The same test in questions 3 to 7 above is applied to population B where the disease is less common. Again, 1,000 patients received both CT scan and test T. 100 patients proved to have the disease with the CT scan. Answer questions 8 to 12. The prevalence of the disease (i.e. proportion of people with the disease) is
9) Since the same test was used, the sensitivity remains the same as in your answer to question 4 above. Amongst the 100 patients with the disease, how many will be tested positive by test T?
10) Since the same test was used, the specificity remains the same as your answer to question 5 above. Amongst the 900 patients free of the disease, how many will be tested POSITIVE by test T?
11) Now, draw a 2 x 2 table with the above figures. What is the positive predictive value in population B (to the nearest %)
12) What is the negative predictive value in population B (to the nearest %)
13) Look at your answers 3 to 12 above. For the same test for the same disease, which of the following measure increases when the prevalence increases (i.e. when the disease becomes more common)?
14) Look at your answers 3 to 12 above. For the same test for the same disease, which of the following measure decreases when the prevalence increases (i.e. when the disease becomes more common)?