There were 821 subjects enrolled in this study. Of the 414 randomized to the treatment (Hydroxychloroquine) arm, 49 (11.8%) developed Covid (or probable Covid) within 14 days of randomization. Of the 407 randomized to the placebo arm, 58 (14.3%) developed Covid (or probable Covid) within 14 days of randomization.

In Homework #3, you reported a sample relative risk of developing COVID for the Hydroxychloroquine group compared to the placebo group of 0.83 with a 95% CI of 0.58 to 1.19.

Suppose you plan to perform a chi-square (or two sample z-test, or Fisher's Exact Test) for this study. What is the null hypothesis for this test in terms of the Risk Difference (RD)?

a. RD=1

b. RD not equal to 1

c. RD = 0

d. RD not equal to 0