6.34 Telemarketing wages. An advertisement in the student newspaper asks you to consider working for a telemarketing company. The ad states, "Earn between $500 and $1000 per week." Do you think that the ad is describing a con?dence interval? Explain your answer.
6.35 Like your job? A Gallup Poll asked working adults about their job satisfaction. One question was "All in all, which best describes how you feel about your job?" The possible answers were "love job," "like job," "dislike job," and "hate job." Fifty-nine percent of the sample responded that they liked their job. Material provided with the results of the poll noted:
Results are based on telephone interviews with 1,001 national adults, aged 18 and older, conducted Aug. 8-11, 2005. For results based on the total sample of national adults, one can say with 95% con?dence
that the maximum margin of sampling error is ±3 percentage points.11
The Gallup Poll uses a complex multistage sample design, but the sample percent has approximately a Normal sampling distribution.
(a) The announced poll result was 59% ± 3%. Can we be certain that the true population percent falls in this interval?
(b) Explain to someone who knows no statistics what the announced result 59% ± 3% means.
(c) This con?dence interval has the same form we have met earlier:
estimate ± z*sestimate
What is the standard deviation sestimate of the estimated percent?
(d) Does the announced margin of error include errors due to practical problems such as undercoverage and nonresponse?