A study (Psychosomatic Medicine 2002; 64: 593–603) claimed that people who consume caffeine regularly may experience higher stress and higher blood pressure. In the experiment, 47 regular coffee drinkers consumed 500 milligrams of caffeine in a pill form (equivalent to four 8-oz cups) during one workday, and a placebo pill during another workday. The researchers monitored the subjects’ blood pressure and heart rate, and the subjects recorded how stressed they felt.
a. Identify the response variable(s), explanatory variable, experimental units, and the treatments.
b. Is this an example of a completely randomized design, or a crossover design? Explain.