The American Journal of Public Health (July 1995)

reported on a population-based study of trauma in Hispanic children. One of the objectives of the study was to compare the use of protective devices in motor vehicles used to transport Hispanic and non-Hispanic white children. On the basis of data collected from the San Diego County Regionalized Trauma System, 792 children treated for injuries sustained in vehicular accidents were classified according to ethnic status

(Hispanic or non-Hispanic white) and seatbelt usage

(worn or not worn) during the accident. The data are summarized in the table below.

a. Calculate the sample proportion of injured Hispanic children who were not wearing seatbelts during the accident.

b. Calculate the sample proportion of injured non-Hispanic white children who were not wearing seatbelts during the accident.

c. Compare the two sample proportions, parts a and b.
Do you think the true population proportions differ?

d. Conduct a test to determine whether seatbelt usage in motor vehicle accidents depends on ethnic status in the San Diego County Regionalized Trauma System. Use a = .01.

e. Construct a 99% confidence interval for the difference between the proportions, parts a and

b. Interpret the interval.