A medical research team wishes to compare a new medicine with a placebo for reducing the symptoms of the common cold.

(a) In the clinical trial, patients are grouped into pairs according to certain criteria such as age, severity of symptoms etc. Then one from each pair is chosen at random and given the new medicine, while the other is given the placebo. Give the correct name for this type of clinical trial, and explain briefly the purpose of grouping patients into pairs.

(b) A student on work experience suggests that patients should instead be divided at random into two groups. Patients in the first group should begin by taking the placebo for a period of time and then the new medicine. Patients in the other group should take the new medicine first and then the placebo. In general, what would be an advantage of this type of design over the one described in part (b)? Explain why this design is, however, not suitable in this case.

(c) In the clinical trial, neither the patients receiving the new medicine nor the patients receiving the placebo know whether they are receiving the medicine or the placebo. The researchers who assess the outcomes of the treatments are also unaware which of the patients are receiving the medicine and which are receiving the placebo. Give the correct name for this type of clinical trial.