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A professor is teaching a large class that has 247 students. He wants to select a sample of 15 students to do a study on the habits of his students. For each of the following sampling methods, explain what kind of method is used (e.g., is it a random sample, nonrandom sample, sample with replacement, sample without replacement, convenience sample, judgment sample, quota sample). a. There are 15 sociology majors in his class. He selects these 15 students to include in the sample. b. He goes through the roster and finds that he knows 30 of the 247 students. Using his knowledge about these students, he selects 15 students from these 30 to include in the sample. c. He enters names of all 247 students in a spreadsheet on his computer. He uses a statistical software (such as Minitab) to select 15 students.

A pharmaceutical company developed a new medicine for compulsive behavior. To test this medicine on humans, the company advertised for volunteers who were suffering from this disease and wanted to participate in the study. As a result, 1820 persons responded. Using their own judgment, the group of physicians who were conducting this study assigned 910 of these patients to the treatment group and the remaining 910 to the control group. The patients in the treatment group were administered the actual medicine, and the patients in the control group were given a placebo. Six months later the conditions of the patients in the two groups were examined and compared. Based on this comparison, the physicians concluded that this medicine improves the condition of patients suffering from compulsive behavior. a. Comment on this study and its conclusion. b. Is this an observational study or a designed experiment? Explain. c. Is this a double-blind study? Explain.