Question

A study of injuries to in-line skaters used data from the National Electronic Injury Surveillance System, which collects data from a random sample of hospital emergency rooms. The researchers interviewed 161 people who came to emergency rooms with injuries from in-line skating. Wrist injuries (mostly fractures) were the most common.

(part a) The interviews found that 55 people were wearing wrist guards and 8 of these had wrist injuries. Of the 106 who did not wear wrist guards, 40 had wrist injuries. Why should we not use the large-sample confidence interval for these data?

A.) One count is only 8, and the guidelines for using the large-sample method call for all counts to be at least 10.

B.) The counts are only 8 and 40, and the guidelines for using the large-sample method call for all counts to be at least 100.

C.) One count is only 8, and the guidelines for using the large-sample method call for all counts to be at least 25.

D.) The counts are only 8 and 40, and the guidelines for using the large-sample method call for all counts to be at least 50.

(part b) The plus four method adds one success and one failure in each sample. What are the sample sizes and counts of successes after you do this? (FILL IN THE BLANKS)

Population	Sample size	Number of successes
wrist guards	_________	__________________
no wrist guards	_________	__________________

(part c) Give the plus four 95% confidence interval for the difference between the two population proportions of wrist injuries. (Use p_guards − p_{no guards} Round your answers to FOUR decimal places.)

_____ to _____

Answer 1

part a

Normal requirement has not met i.e sample size is at least 10. so correct choice is option A

A.) One count is only 8, and the guidelines for using the large-sample method call for all counts to be at least 10.

part b

Using plus four method, number of successes in first sample is and sample size is

The number of successes in first sample is and sample size is

Population	Sample size	Number of successes
wrist guards	57	9
no wrist guards	108	50

part c