Sample surveys on sensitive issues can give different results depending on how t

Question

Sample surveys on sensitive issues can give different results depending on how the question is asked. A University of Wisconsin study divided 2400 respondents into 3 groups at random. All were asked if they had ever used cocaine. One group of 800 was interviewed by phone; 163 said they had used cocaine. Another 800 people were asked the question in a one-on-one personal interview; 205 said "Yes." The remaining 800 were allowed to make an anonymous written response; 219 said "Yes." Are there statistically significant differences among these proportions? Carry out a chi-square test for association between how the question is asked and the response regarding cocaine use. Test H0:H0: the proportion of people who admit cocaine use is the same for all three interview methods versus Ha:Ha: the proportions are not the same (interview type makes a difference). Use =0.01

. 2(±0.0001)=_________)= P(±0.0001)=_________ There is evidence that interview type makes a difference There is no evidence that interview type makes a difference

Explanation / Answer

  2 =11.4922

P =0.0032

_ There is evidence that interview type makes a difference

Observed O phone personal written Total used 163 205 219 587 not used 637 595 581 1813 Total 800 800 800 2400 0.244583 Expected E=rowtotal*column total/grand total phone personal written Total used 195.67 195.67 195.67 587 not used 604.33 604.33 604.33 1813 Total 800 800 800 2400 chi square =(O-E)^2/E phone personal written Total used 5.454 0.4452 2.7825 8.681 not used 1.766 0.144 0.901 2.811 Total 7.219 0.589 3.683 11.4922

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