A consumer producttesting organization compared the annual p

A consumer product-testing organization compared the annual power consumption for five different brands of dehumidifier. As far as possible, comparable models were chosen from each manufacturer. Eight units of each model were purchased from randomly-chosen retail outlets. Because power consumption depends on the prevailing humidity level, each model was tried at four different levels, ranging from moderate to high humidity, two units being assigned at random to each humidity level. The table below shows annual power consumption in kwh for each of the 40 units tested

Humidity

1

2

3

4

Brand

1

661, 690

779, 782

848, 833

841, 854

2

760, 732

791, 788

878, 894

983, 953

3

742, 751

806, 808

906, 902

984, 953

4

775, 827

879, 887

931, 950

1029, 970

5

842, 795

956, 916

983, 989

1012, 1039

Determine whether brand significantly affects power consumption of the dehumidifier

Solution

The interaction is not significant at the 5% level (P = 0.058), so we can proceed to test the main effects, both of which are highly significant. Hence we conclude that the annual power consumption of dehumidifiers varies with brand and with the level of humidity, but the response to humidity is the same for each brand tested.