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The evidence supporting obesity as a risk factor for coloncancer remains inconclusive, especially among women. A studyreported the association between obesity (measured at baseline) andcolon cancer morbidity as determined from review of medical recordsand death certificates in a nationally representative cohort of menand women age 25-74 years who participated in the First NationalHealth and Nutrition Examination Survey from 1971 to 1975 and weresubsequently followed up through 1992. The following table is fromthis study for men and women combined.

Baseline body mass index (kg/height)2	Number of incident cases of colon cancer	Person-years of follow up	Crude incidence rate/100,000 PY
<22	29	54,475
22-<24	42	39,919
24-<26	37	37,610
26-<28	41	33,635
28-<30	36	22,122
30+	43	35,904

a. Which of the following best describes the research designused in this study? Choose the ONE best answer. (1 point)

1. Cross-sectional survey
2. Ecological study
3. Population based case control study
4. Cohort study
5. None of the above

b. Complete the table above by calculating the crude body massindex-specific incidence rates. (Show your work in the tableabove.) (3 points – ½ point for each correct answer)

c. Calculate the relative risk (rate ratio) of colon cancerassociated with a BMI of 30+. Use the lowest BMI category as thereference group. In one sentence interpret your answer. (2points)

d. Calculate the attributable fraction among those in the 30+BMI category. In one sentence interpret your answer. (Theattributable fraction formulas provided in class can be used eventhough the data provided here is for rates.) (2 points)