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.”

1. Was this an experiment or an observational study? Justify your answer.

We have been given that:

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.”

Since,

Experimental Study: In experimental studies, the researcher has control over the variables. He exploits variables in order to make changes in the study, whereas for

Observational Study: In observational studies, the researcher does not control the research environment, he simply observes.

Since the researcher merely observes the value of subject and concludes his experiment. Therefore it's safe to say that the study conducted is observational.