Exercise and heart attacks Refer to Exercise 4.68. One potential confounding variable was the amount of exercise the physicians got. The randomization should have balanced the treatment groups on exercise. The contingency table shows the relationship between whether the physician exercised vigorously and the treatments.

a. Find the conditional proportions (recall Section 3.1) in the categories of this potential confounder (amount of exercise) for each treatment group. Are they similar?

b. Do you think that the randomization process did a good job of achieving balanced treatment groups in terms of this potential confounder? Explain.

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Exercise Vigorously? Treatment Yes No Total Aspirin 7,910 2,997 10,907 Placebo 7,861 3,060 10,921