Will taking antioxidants help prevent colon cancer? People who eat lots of fruit

Question

Will taking antioxidants help prevent colon cancer?

People who eat lots of fruits and vegetables have lower rates of colon cancer than those who eat little of these foods. Fruits and vegetables are rich in antioxidants such as vitamins A, C, and E. A clinical trial studied this question with 864 people who were at risk of colon cancer. The subjects were divided into four groups: daily beta carotene, daily vitamins C and E, all three vitamins every day, and daily placebo. After four years, the researchers were surprised to find no significant difference in colon cancer among the groups.

(a) Is this an observational study or an experiment? Why?

(b) What are the factor(s)?

(c) What is the response variable?

(d) What does no significant difference mean in describing the outcome of the study?

(e) Name some lurking variable that could explain why people who eat lots of fruits and vegetables have lower rates of colon cancer. The experiment suggests that these variables, rather than the antioxidants, may be responsible for the observed benefits of fruits and vegetables.

Explanation / Answer

a) This is an experiment

b) i) randomly assign the 865 people to four groups of 216 people

ii) give each of the subjects in the four groups a treatment – either daily beta carotene, daily vitamin C and E, all three vitamins, or a daily placebo – for 4 years

iii) compare rates of colon cancer among the different groups

c) Response variable – colon cancer

d) “No significant difference” means that there was no difference beyond what would be expected due to chance variation

e) Variables related to healthier lifestyle.

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