Consider the study from question 2, and other studies comparing an outcome (binary,

continuous, or time to event) between two (or more) populations. For such studies, based

on random samples from such populations, why are confidence intervals used?

a. Confidence intervals account for the uncertainty in sample estimates that comes from

the random variation in such estimates across different studies of the same size.

b. Confidence intervals guarantee that the study results will be scientifically useful.

c. Confidence intervals help validate that a study was well designed.

d. Confidence intervals account for uncertainty that arises because of problems with the

study: for example, people answering a question incorrectly, or a data entry error