A recent study by all Allstate Insurance Co. finds that 82% of teenagers have used cell phones while driving. In October 2010, Massachusetts enacted a law that forbids cell phone use by drivers under the age of 18. A policy analyst would like to determine whether the law has decreased the proportion of drivers under the age of 18 who use a cell phone.
a) State the null and the alternative hypothesis to test the policy analyst's objective.
b) Suppose the sample of 200 drivers under the age of 18 results in 150 who still use a cell phone while driving. What is the value of the test statistic? What is the p-value?
c) At a=0.05 has the law been effective?
d) Repeat the exercise using the critical value approach with a=0.05.