Question: Refer to Exercise. In each case, explain whether a control group was used and whether a placebo treatment was used.

Exercise: Explain whether each of the following experiments was single-blind, double-blind, or neither.

a. An electric company wanted to know whether residential customers would use less electricity during peak hours if they were charged more during those hours. One hundred customers were randomly selected to receive the special time-of-day rates, and they were matched with 100 customers who were similar in terms of past electrical use and household size. Special meters were installed for all 200 customers, and at the end of three months, the usage during peak hours was compared for each pair. The technician who read the meters did not know who had which rate plan.

b. To test an herbal treatment for depression, 100 volunteers who suffered from mild depression were randomly divided into two groups. Each person was given a month's supply of tea bags. For one group, the tea contained the herb mixed with a spice tea; for the other group, the bags contained only the spice tea. Participants were not told which type of tea they had and were asked to drink one cup of the tea per day for a month. At the end of the month, a psychologist evaluated them to determine whether their mood had improved. The psychologist did not know who had the tea with the herbal ingredient added.

c. To compare three packaging designs for a new food, a manufacturer randomly selected three grocery stores in each of 50 cities. The three designs were randomly assigned to the three stores in each city, and sales were compared for a 2-month period.