Give a 95% confidence interval for the proportion of all drivers who ran one or more of the last ten red lights they encountered. (b) Nonresponse is a practical problem for this survey—only 21.6% of calls that reached a live person were completed. Another practical problem is that people may not give truthful answers. What is the likely direction of the bias: do you think more or fewer than 171 of the 880 respondents really ran a red light? Why?
A random digit dialing telephone survey of 880 drivers asked, “Recalling the last ten
traffic lights you drove through, how many of them were red
when you entered the intersections?” Of the 880 respondents,
171 admitted that at least one light had been red.
(a) Give a 95% confidence interval for the proportion of all
drivers who ran one or more of the last ten red lights they
encountered.
(b) Nonresponse is a practical problem for this survey—only
21.6% of calls that reached a live person were completed.
Another practical problem is that people may not give truthful answers. What is the likely direction of the bias: do you
think more or fewer than 171 of the 880 respondents really
ran a red light? Why?
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