Sample surveys on sensitive issues can give different results depending on how the question is asked. A University of Wisconsin study randomly divided 2400 respondents into three groups. All participants were asked if they had ever used cocaine. One group of 800 was interviewed by phone; 21% said they had used cocaine. Another 800 people were asked the question in a one-on-one personal interview; 25% said “Yes.” The remaining 800 were allowed to make an anonymous written response; 28% said “Yes.”10 1. Was this an experiment or an observational study? Justify your answer. 2. Make a two-way table of responses about cocaine use by how the survey was administered. 3. Are the differences between the three groups statistically significant? Give appropriate evidence to support your answer
Sample surveys on sensitive issues can give different results depending on how the question is asked. A University of Wisconsin study randomly divided 2400 respondents into
three groups. All participants were asked if they had ever used cocaine. One group of 800
was interviewed by phone; 21% said they had used cocaine. Another 800 people were
asked the question in a one-on-one personal interview; 25% said “Yes.” The remaining 800
were allowed to make an anonymous written response; 28% said “Yes.”10
1. Was this an experiment or an observational study? Justify your answer.
2. Make a two-way table of responses about cocaine use by how the survey was administered.
3. Are the differences between the three groups statistically significant? Give appropriate
evidence to support your answer
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