In-line skaters. A study of injuries to in-line skaters used data from theNational

Chapter 0, Problem 21.4

(choose chapter or problem)

In-line skaters. A study of injuries to in-line skaters used data from theNational Electronic Injury Surveillance System, which collects data from arandom sample of hospital emergency rooms. The researchers interviewed161 people who came to emergency rooms with injuries from in-line skating.Wrist injuries (mostly fractures) were the most common.7(a) The interviews found that 53 people were wearing wrist guards and 6 of thesehad wrist injuries. Of the 108 who did not wear wrist guards, 45 had wrist injuries.Why should we not use the large-sample confidence interval for these data?(b) Give the plus four 95% confidence interval for the difference between thetwo population proportions of wrist injuries. State carefully what populations yourinference compares. We would like to draw conclusions about all in-line skaters,but we have data only for injured skaters.