Consider the following two 2 × 2 tables:

a. Calculate the proportion of failures for all four treatments.
b. Calculate the difference in proportions of failure between Treatments A and B. Then do the same calculation to compare Treatments C and D.

c. Calculate the relative risk of failure between Treatments A and B. Then do the same calculation to compare Treatments C and D.
d. Which pair of treatments do you think produce responses that are more different: A and B or C and D?

e. Which statistic reflects your answer to part (d): difference in proportions or relative risk? Explain.

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Treatment A Treatment B Success 90 98 Failure 10 2 Total 100 100 Treatment C Treatment D Success 40 48 Failure 60 52 Total 100 100