5.17 Conserving energy. Example 5 describes an experiment to learn whether providing households with electronic meters or with an app will reduce their electricity consumption. An executive of the electric company objects to including a control group. He says, “It would be cheaper to just compare electricity use last year [before the meter or app was provided] with consumption in the same period this year. If households use less electricity this year, the meter or app must be working.” Explain clearly why this design is inferior to that in Example 5.