Lack of sleep costs companies about $18 billion a year in lost productivity, according to the National Sleep Foundation. Companies are waking up to the problem, however. Some even have quiet rooms available for study or sleep. "Power naps" are in vogue (Athens Daily News, Jan. 9, 2000). A major airline recently began encouraging reservation agents to nap during their breaks. The accompanying table lists the number of complaints received about each of a sample of 10 reservation agents during the 6 months before naps were encouraged and during the 6 months after the policy change.
a. Do the data present sufficient evidence to conclude that the new napping policy reduced the mean number of customer complaints about reservation agents? Test using α = .05.
b. What assumptions must hold to ensure the validity of the test?
c. What variables, not controlled in the study, could lead to an invalid conclusion?

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OperatorBefore Policy After Policy 10 16 7 14 9 10