Researchers in Germany tested the effect of a dietary supplement designed to control metabolism in patients with type 2 diabetes. Thirty-one patients with type 2 diabetes completed the study. The patients were assigned at random either the supplement or a placebo for 12 weeks. After a subsequent “wash-out” period of 12 weeks, the patients were assigned the other product. At the conclusion of the study, the patients’ glycated hemoglobin, fasting blood glucose, and fructosamine levels were checked, as well as their lipid parameters. (Source: Food and Nutrition Research).

(a) Identify the experimental units and treatments used in this experiment.

(b) Identify a potential problem with the experimental design being used and suggest a way to improve it.

(c) The experiment is described as a placebo-controlled, double-blind study. Explain what this means.

(d) How could blocking be used in designing this experiment?