1.19 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 th
rest were evenly divided between 1g Vitamin C, 3g Vitamin C, or 3g Vitamin C plus additive
to be taken at onset of a cold for the following two days. All tablets had identical appearan
and packaging. The nurses who handed the prescribed pills to the patients knew which patie
received which treatment, but the researchers assessing the patients when they were sick did n
No significant differences were observed in any measure of cold duration or severity between
four medication groups, and the placebo group had the shortest duration of symptoms.
(a) Was this an experiment or an observational study? Why?
(b) What are the explanatory and response variables in this study?
(c) Were the patients blinded to their treatment?
(d) Was this study double-blind?
(e) Participants are ultimately able to choose whether or not to use the pills prescribed to
We might expect that not all of them will adhere and take their pills. Does this introd
confounding variable to the study? Explain your reasoning.
of you

a) It cannot be described as an Observational study because the elements of control were present. The control group was the group who were given placebos.

The other answers are:

b) The explanatory variable is Vitamin C that was administered.

c) Yes, the patients were blinded to their treatment because they had no information about which grammage of vitamin c they were given or whether it was even a placebo. All the pills were identical.

d) Yes. Double-blind in research is a type of clinical trial where neither the participants nor the researcher as the details of the intervention being given until the trial is over. This helps to reduce bias.

e) Yes it does introduce confounding variables in the study. A confounding variable is that which affects other variables in such a manner that creates a distortion of association between the dependent and independent variables. This was almost unavoidable because the pill had to be taken at the onset of a cold.

What is an Observational Study?

The key factor about Observational Studies is that they occur without interference by the researcher. The second is that the participants are observed in their natural state or behavior.