The manufacturer of a new vitamin (vitamin X) decides to sponsor a study to determine the vitamin's effectiveness in curing the common cold. Five hundred out of the 50,000 college students in a large city were paid to participate as subjects in this study. All the participating subjects were suffering from a cold at the start of the study. The subjects were each given two tablets of vitamin X a day. Based on information provided by the subjectsthemselves, 457 out of the 500 subjects were cured of their colds within 3 days. (The average number of days a cold lasts is 4.87days.) As a result of this study, the manufacturer launched an advertising campaign based on the claim that "vitamin X is more than 90% effective in curing the common cold."

(a) Was the study a controlled study? Explain. 

(b) List three possible causes other than the effectiveness of vitamin X itself that could have confounded the results of the study.

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a A controlled study is an investigation wherein members are isolated into two gatherings the treatm... View the full answer