To refine the experiment described in Exercise 16.15, a psychologist added an additional set of households to each group. This group had a special meter installed to show them exactly how fast their electric bill was increasing. (The amount-to-date was displayed on the meter.)

The data follow; the nonmetered data are the same as those in Exercise 16.15.

Y C Y C Y C Nonmetered 58 75 60 70 75 80 25 40 30 25 60 55 50 68 55 65 70 73 40 62 50 50 65 61 55 67 45 55 55 65 Metered 25 42 40 55 55 56 38 64 47 52 62 74 46 70 56 68 57 60 50 67 28 30 50 68 55 75 55 72 70 76

a. Run the analysis of covariance on these data—after first checking the assumption of homogeneity of regression.

b. Draw the appropriate conclusions.