15.12 The data for this exercise are from a sample of twelfth-graders, collected as part of the 2001 Youth Risk Behavior Surveillance System. The students were asked how often they wear a seatbelt while driving, and for this exercise, we combine the responses for “never” and “rarely” and for “most times” and “always”

and ignore the “sometimes” responses. A contingency table of the results for males and females follows.

Seatbelt Use Most Times or Always Rarely or Never Total Female 964 97 1061 Male 924 254 1178 Total 1888 351 2239 Data source: http://www.cdc.gov/nccdphp/dash/yrbs/.

a. Calculate the row percentages for females and the row percentages for males. Compare them.

b. Specify the null and alternative hypotheses that could be tested by using a chi-square statistic in this situation. Make sure you specify the population to which they apply.

c. Calculate the expected count for the cell “Male, Most times or Always.”

d. Using the expected count you calculated in part (c), obtain the expected counts for the remaining cells by subtraction.
Remember that row and column totals are the same for expected counts as they are for observed counts.

e. Compute the chi-square statistic.

f. Use the chi-square statistic computed in part

(e) to find a p-value or p-value range.
g. Form a conclusion, and write it in the context of the situation.
Be sure to state the level of significance that you are using.