Question

1.32 vitamin supplements: 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 1g vitamin c, 3g vitamin c, or 3g 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 observational study?
experiment
observational
b) what is the explanatory variable?
volunteers
level of vitamin c supplement
duration of cold
severity of cold
c) what is the response variable?
volunteers
severity of cold
duration of cold
level of vitamin c supplement
d) were the patients blind to their treatment?
yes

Explanation:

a) An experiment involves manipulating a variable. Here, different vitamin - C treatments and a placebo were assigned, so it's an experiment.
b) The explanatory variable is what is being manipulated or changed to see its effect. Here, it's the level of vitamin C supplement.
c) The response variable is what is being measured as a result of the manipulation. Here, it's the duration or severity of the cold.
d) Since all tablets had identical appearance and packaging, the patients were blind to their treatment.

Answer:

a) Experiment
b) level of vitamin C supplement
c) duration of cold, severity of cold
d) Yes