Lung cancer mortality was 0.57 per 1,000 per year among light smokers and 0.07 among nonsmokers. What is the attributable proportion?

1. The attributable proportion takes the excess in the exposed group as a share of the exposed group's own level. 2. Subtract the unexposed rate from the exposed rate: 0.57 minus 0.07 equals 0.50. 3. Divide by the exposed rate: 0.50 divided by 0.57 equals 0.877. 4. Multiplying by 100 gives 87.7%, so about 88% of the lung cancer among these smokers is attributable to smoking. 5. The remaining 12.3% would have occurred anyway, which is why that figure appears as a distractor. 6. 714.3% divides the excess by the unexposed rate instead of the exposed rate. 7. 81.4% is the rate ratio of 8.14 with the decimal point shifted, so it skips the subtraction step entirely. _Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Definition of attributable proportion_