In this article, the researchers reported both a risk difference (RD) and a relative risk (RR) and 95% confidence intervals for each. However, only one p-value was reported, the p-value from the chi-square test, and this p-value is less than 0.01. Why do the researchers only report one p-value, but two confidence intervals for the two different measures of association?

a. This is a mistake; the researchers should report two separate p-values for testing Ho: RD =0, and Ho: RR=1 , respectively.

b. Because the p-value reported is statistically significant. As such the researchers were worried that had they computed a 2nd p-value, it would be greater than 0.05, and this article would never have been published.

c. Because Ho: RD=0 and Ho: RR=1 are two different ways of expressing the same null hypothesis of equal proportions of STI testing in the Intervention and control groups at the population level.

d. Because the p-value and the confidence intervals are different ways of making inferences about the "truth" in the population,