Textbook Questions: Rebecca Newton 1. Calculate the etiologic fraction when the RR for disease associated with aa given exposure is 1.2, 1.8.3, and 15. (RR-1)/RR (1.2-1)/1.2=0.2/1.2= 16.7% (1.8-1)/1.8= 0.8/1.8= 44.4% (3-1)/3= 2/3 = 66.7% (15-1)/15= 14/15 = 93.3% 2. The impact of an exposure on a population does not depend upon: 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 formula for RR. 3. What is the RR of dying of lung cancer for smokers vs nonsmokers? Smokers Non-Smokers Lung Cancers (Yes) 71 (A) 7 (C) 78 .55x 100,000 = population of smokers 55,000 55,000-71= those who do not have cancer [71/(71+54,929)] / [7/(7+44,993)] Risk of dying of lung cancer 71/55,000/7/45,000 Lung Cancer (No) 54,929 (B) 44,993 (D) 99,922 Total 55,000 45,000 100,000 0.0012909091/ 0.0001555555= RR 8.30 4. What is the RR of dying of coronary thrombosis for smokers versus nonsmokers? Smokers Non-Smokers C. Thrombosis (Yes) 599 (A) 422 (B) 1,021 C. Thrombosis (No) 54,401 44,578 98,979 Total 55,000 45,000 100,000 .55x 100,000 = population of smokers 55,000 [599/ (599+54,401)]/ [422/(422+44,993)] =599/55,000/422/45,000= 0.0108909091/0.0093777778= RR 1.16 5. What is the etiologic fraction of disease due to smoking among individuals with lung cancer? Formula (Ie-Ine)/ Ie (71-7)/71= 64/71=0.90 6. What is the etiologic fraction of disease due to smoking among individuals with coronary thrombosis? Formula (Ie-Ine)/ Ie (599-422)/599= 177/599=0.30 7. What is the population etiologic fraction of lung cancer due to smoking? Population etiologic fraction= Pe (RR-1)/ Pe (RR-1)+1 x 100 .55(8.30-1)/.55 (8.30-1) +1x100 .55 (7.30)/.55 (7.30) + 1 x 100 4.015/5.015x100= 80.06% 8. What is the population etiologic fraction of coronary thrombosis due to smoking? Population etiologic fraction= Pe (RR-1)/ Pe (RR-1)+1 x 100 .55(1.16-1)/.55 (1.16-1) +1x100 .55 (0.16)/.55 (0.16) + 1 x 100 0.088/1.088x100= 8.088% 9. On the basis of RR and etiologic fractions associated with smoking from lung cancer and coronary thrombosis, which one of the following statements is most likely to be correct? a. Smoking seems much more likely to be causally related to coronary thrombosis than to lung cancer. b. Smoking seems much more likely to be casually related to lung cancer than to coronary thrombosis. c. Smoking seems much more likely to be casually related to both lung cancer and coronary thrombosis. d. Smoking does not seem to be causally related to either lung cancer or coronary thrombosis. e. No comparative statement is possible between smoking and lung cancer or coronary thrombosis