Does regular exercise reduce the risk of a heart attack in males over 40 years of age? Here are two ways to study this question.

STUDY A: A medical researcher finds 2000 men over 40 who have had heart attacks. She also finds 2000 men over 40 who have not had a heart attack. She asks each man in each group whether they exercised regularly as part of his usual lifestyle.

STUDY B: Another researcher finds 4000 men over 40 who have not had heart attacks and are willing to participate in a study. She assigns 2000 of the men to a regular program of supervised exercise. The other 2000 continue their usual habits. The researcher follows both groups for three years.

a) Name the explanatory and response variables in this study.

b) What type of study design is used in each of Study A and Study B?

c) Which design will produce more trustworthy data? Explain why.

d) Draw a schematic diagram to outline the design above that is an experiment.