A beverage distributor wanted to determine the combination of advertising agency (two levels) and advertising medium (three levels) that would produce the largest increase in sales per advertising dollar. Each of the advertising agencies prepared ads as required for each of the media-- newspaper, radio, and television. Twelve small towns of roughly the same size were selected for the experiment, and two each were randomly assigned to receive an advertisement prepared and transmitted by each of the six agency-medium combinations. The dollar increases in sales per advertising dollar, based on a 1-month sales period, are shown in the table.
Advertising Medium
The SPSS analysis is shown below.
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* * * A N A L Y S I S O F V A R I A N C E * * *
SALES
BY AGENCY
MEDIUM
Sum of
Mean
Signif
Source of Variation
Squares
DF
Square
F
of F
Main Effects
238.299
3
79.433
13.934
.004
AGENCY
39.967
1
39.967
7.011
.038
MEDIUM
198.332
2
99.166
17.395
.003
AGENCY*MEDIUM
77.345
2
38.672
6.784
.029
Explained
315.644
5
63.129
11.074
.005
Residual
34.205
6
5.701
Total
349.849
11
31.804
(Note: SPSS uses "Explained" instead of "Treatment" in the factorial analysis. Also, SPSS uses "Residual" instead of "Error.") Would you test the main effects factors, agency and medium, in this example? Explain why or why not.
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