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Unformatted text preview: College of Human Ecology Cornell University Ithaca, New York Department of Policy Analysis and Management PAM 210 Intro Stats A. Sinan ¨ Un¨ur – Spring 2008 Prelim 2 – Answers March 27, 2008 Multiple Choice MC 1) Suppose you were to read about a study showing that people who sleep less than five hours a night have twice as much risk of a premature death as people who sleep seven or eight hours a night. Which of the following is NOT an example of a possible “confounding variable” in this study? ( a ) Medications a person is taking. ( b ) The amount of alcohol a person drinks in the evening. ( c ) The amount of sleep a person gets per night. ( d ) The amount of stress a person is under in their work. Answer : 1c . The amount of sleep a person gets per night is an explanatory variable whereas the others may all effect the risk of premature death. MC 2) A new headache remedy was given to a group of 25 participants who had headaches. Four hours after taking the new remedy, 20 of the participants reported that their headaches had disappeared. From this information you conclude: ( a ) nothing, because there is no control group for comparison. ( b ) that the remedy is effective for the treatment of headaches. ( c ) nothing, because the sample size is too small. ( d ) that the remedy is not effective for the treatment of headaches. Answer : 2a . Without a control group, we cannot know if those people’s symptoms disap- peared thanks to the remedy or would have disappeared anyway in that time period even if they had not taken the medication or if the said remedy actually extended the time to recovery. MC 3) A controlled experiment is usually preferred to an observational study because ( a ) It is easier to collect data from an experiment than it is from an observational study. ( b ) It is cheaper to run an experiment than it is to do an observational study. ( c ) Cause-and-effect conclusions can only be drawn based on controlled experiments. ( d ) Volunteers can be used for an experiment but not for an observational study. Answer : 3c . MC 4) For a study of dietary habits of Americans, a simple random sample of 1,000 people were selected and sent a survey by mail. 347 out of these people completed and returned the survey to the researchers. The results of this study, if applied to all Americans, are ques- tionable because ( a ) the researchers did not attempt to contact all Americans. ( b ) the researchers should have chosen people who were likely to respond rather than using random sampling. ( c ) selection bias. ( d ) nonresponse bias Answer : 4d . We do not (and cannot) know why the people who did not respond did not respond and whether the reasons they did not respond had anything to do with their dietary habits....
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This note was uploaded on 05/13/2008 for the course PAM 2100 taught by Professor Abdus,s. during the Spring '08 term at Cornell.
- Spring '08