Like many behaviours, the proportion of drivers who use seat belts varies with factors such as age, sex, ethnicity and local laws. As part of a broader study, investigators observed a random sample of 117 female, Hispanic drivers in Boston; of these, 68 used their seat belts. What is the proportion of seat belt users in this sample? What is the proportion of non-users? Show that calculation of confidence intervals (CI) is legitimate for this sample (i.e. that use of the Normal approximation to the binomial is safe) then calculate the 95% and 99% CIs for the proportion of all female Hispanic drivers in Boston who wear seatbelts. Why is the 99% CI wider than the 95% CI?