People who get lots of vitamins by eating five or more servings of fresh fruit and vegetables each day (especially "cruciferous" vegetables like broccoli)

have much lower death rates from colon cancer and lung cancer, according to many observational studies. These studies were so encouraging that two randomized controlled experiments were done. The treatment groups were given large doses of vitamin supplements, while people in the control groups just ate their usual diet. One experiment looked at colon cancer; the other, at lung cancer.

The first experiment found no difference in the death rate from colon cancer between the treatment group and the control group. The second experiment found that beta carotene (as a diet supplement) increased the death rate from lung cancer. 23 True or false, and explain:

(a) The experiments confirmed the results of the observational studies.

(b) The observational studies could easily have reached the wrong conclu-

sions, due to confounding—people who eat lots of fruit and vegetables have lifestyles that are different in many other ways too. plo47