Question

The evidence supporting obesity as a risk factor for colon cancer remains inconclusive, especially among women. A study reported the association between obesity (measured at baseline) and colon cancer morbidity as determined from review of medical records and death certificates in a nationally representative cohort of men and women age 25-74 years who participated in the First National Health and Nutrition Examination Survey from 1971 to 1975 and were subsequently followed up through 1992. The following table is from this 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 design used 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 mass index-specific incidence rates. (Show your work in the table above.) (3 points – ½ point for each correct answer)

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

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

Answer 1

a)Cohort Study.

b)

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	105.213
24-<26	37	37,610	98.378
26-<28	41	33,635	121.897
28-<30	36	22,122	162.733
30+	43	35,904	119.764

c)A relative risk or rate ratio measures the relativeness of an exposed group(in our case BMI 30+) with a reference or an unexposed group( in our case with the lowest SIR,i.e., BMI 24<26). It is used for comparison.

Final Ans: 0.821

Interpretation: Women with BMI 30+ have 0.821 times more chance of having colon cancer than as compared to those with BMI 24<26.

d)Apolgies but I cn't seem to find this one. Although I will try to get the answer.