Question

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, 168 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 10 red lights they encountered. (Use the plus four method. Round your answers to four decimal places.)
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(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 168 of the 880 respondents really ran a red light? Why?

It is likely that more than 171 respondents have run red lights. We would not expect very many people to claim that they have run red lights when they have not, but some people will deny running red lights when they have.It is likely that less than 171 respondents have run red lights. We would not expect very many people to deny running red lights when they have, but some people will claim that they have run red lights when they have not.    

Answer 1