Questions: In order to assess the effectiveness of taking large doses of vitamin C in reducing the duration of the common cold, researchers recruited 400 healthy volunteers from staff and students at a university. A quarter of the patients were assigned a placebo, and the rest were evenly divided between 1 g Vitamin C, 3 g Vitamin C, or 3 g Vitamin C plus additives to be taken at onset of a cold for the following two days. All tablets had identical appearance and packaging. The nurses who handed the prescribed pills to the patients knew which patient received which treatment, but the researchers assessing the patients when they were sick did not. No significant differences were observed in any measure of cold duration or severity between the four medication groups, and the placebo group had the shortest duration of symptoms. a) Was this an experiment or an observational study? Why? Observational study, as each patient determined their own treatment. Experiment, as the treatment was assigned to each patient. b) What is the explanatory variable in this study? the number of patients in the study duration of the cold the amount of Vitamin C given c) What is the response variable in this study? the number of patients in the study duration of the cold the amount of Vitamin C given d) Were the patients blinded to their treatment? No Yes

Transcript text: In order to assess the effectiveness of taking large doses of vitamin C in reducing the duration of the common cold, researchers recruited 400 healthy volunteers from staff and students at a university. A quarter of the patients were assigned a placebo, and the rest were evenly divided between 1 g Vitamin C, 3 g Vitamin C, or 3 g Vitamin C plus additives to be taken at onset of a cold for the following two days. All tablets had identical appearance and packaging. The nurses who handed the prescribed pills to the patients knew which patient received which treatment, but the researchers assessing the patients when they were sick did not. No significant differences were observed in any measure of cold duration or severity between the four medication groups, and the placebo group had the shortest duration of symptoms. a) Was this an experiment or an observational study? Why? Observational study, as each patient determined their own treatment. Experiment, as the treatment was assigned to each patient. b) What is the explanatory variable in this study? the number of patients in the study duration of the cold the amount of Vitamin C given c) What is the response variable in this study? the number of patients in the study duration of the cold the amount of Vitamin C given d) Were the patients blinded to their treatment? No Yes