Utility companies. Example 3.21 describes an experiment to learn whether providing households with electronic meters or charts will reduce their electricity consumption.

An executive of the utility company objects to including a control group. He says, “It would be simpler to just compare electricity use last year (before the meter or chart was provided) with consumption in the same period this year. If households use less electricity this year, the meter or chart must be working.” Explain clearly why this design is inferior to that in Example 3.21.