The incidence rate ratio (and 95% confidence interval) of recovery for the remdesivir group compared to the placebo group is 1.29 (1.12, 1.49).

The reported 95% confidence interval (CI) for the population level IRR is not perfectly symmetric around the estimated IRR.Why is this?

a. This is a mistake: the 95% CI for a ratio must be symmetric around the estimated ratio.

b. The researchers reported a 99% CI instead of a 95% CI.

c. Confidence intervals for ratios are not necessarily symmetric around the sample estimate on the ratio scale, but they are on (natural) log ratio scale.

d. Because this is a small study, a t-correction was used to create the confidence interval.