Chapter 9 9-2 Textbook Questions

Chapter 9: 9-2 Textbook Questions 1. Calculate the etiologic fraction when the RR for disease associated with a given exposure is 1.2, 1.8, 3, and 15. A. Relative Risk (RR) = 1.2 (1.2 - 1) / 1.2 = 0.1666 etiologic fraction = 0.1666 B. Relative Risk (RR) = 1.8 (1.8 - 1) / 1.8 = 0.4444 etiologic fraction = 0.4444 C. Relative Risk (RR) = 3 (3 - 1) / 3 = 0.6666 etiologic fraction = 0.6666 D. Relative Risk (RR) = 15 (15-1) / 15 = 0.933 etiologic fraction = 0.933 2. The impact of an exposure on a population does not depend on: A. the strength of the association between exposure and disease. B. the prevalence of the exposure. C. the case fatality rate. D. the overall incidence rate of disease in the population. The next seven questions (3–9) are based on the following data: The death rate per 100,000 for lung cancer is 7 among nonsmokers and 71 among smokers. The death rate per 100,000 for coronary thrombosis is 422 among nonsmokers and 599 among smokers. The prevalence of smoking in the population is 55%. (If necessary, refer to the chapter on cohort studies for formulas for RR.) 3. What is the RR of dying of lung cancer for smokers versus nonsmokers? The RR of dying of lung cancer for smokers versus nonsmokers is Lung cancer death rate for smokers = 71 / 100,000 Lung cancer death rate for nonsmokers = 7 / 100,000 (71/100,000) / (7/100,000) Relative Risk (RR) = 10.14 4. What is the RR of dying of coronary thrombosis for smokers versus nonsmokers? The RR of dying of coronary thrombosis for smokers versus nonsmokers is Coronary thrombosis death rate for smokers = 599 / 100,000 Coronary thrombosis death rate for nonsmokers = 422 / 100,000 (599/100,000) / (422/100,000) Relative Risk (RR) = 1.41 5. What is the etiologic fraction of disease due to smoking among individuals with lung cancer? The etiologic fraction of disease due to smoking among individuals with lung cancer is [(71 / 100,000 – 7 / 100,000)] / 71 / 100,000 0.00071-0.00007 / 0.00071 etiologic fraction = 0.90 6. What is the etiologic fraction of disease due to smoking among individuals with coronary thrombosis? The etiologic fraction of disease due to smoking among individuals with coronary thrombosis is (599 / 100,000) – (422 / 100,000) / (599 / 100,000) = (0.00599) – (0.00422) / (0.00599) (0.00177) / (0.00599) etiologic fraction = 0.30 7. What is the population etiologic fraction of lung cancer due to smoking? The population etiologic fraction of lung cancer due to smoking is 0.55 (10.14 – 1) / 0.55 (10.14 – 1) +1] X 100 [0.55 (9.14) / 0.55 (9.14) +1] X 100 [5.027 / (5.027 + 1)] X 100 [5.027 / 6.027] X 100[0.83] X 100 population etiologic fraction = 83% 8. What is the population etiologic fraction of coronary thrombosis due to smoking? The population etiologic fraction of coronary thrombosis due to smoking [0.55 (1.4 – 1) / 0.55 (1.4 – 1) + 1] X 100 [0.55 (0.4) / 0.55 (0.4) + 1] X 100 [0.22 / (0.22 + 1)] X 100 [0.22 / 1.22] X 100 [0.18] X 100 population etiologic fraction = 18%