Page 189 - [Uma_Sekaran]_Research_methods_for_business__a_sk(BookZZ.org)

FACTORIAL DESIGN 173

Figure 7.11
Illustration of a 3 × 3 factorial design.

Bus Fare Reduction Rates
Type of Bus 5c 7c 10c
Luxury Express X 1 Y 1 X 2 Y 1 X 3 Y 1
Standard Express X 2 Y 2 X 1 Y 2 X 3 Y 2
Regular X 3 Y 3 X 2 Y 3 X 1 Y 3

FACTORIAL DESIGN

Thus far we have discussed experimental designs in the context of examining a
cause-and-effect relationship between one independent variable and the depen-
dent variable. The factorial design enables us to test the effects of two or more
manipulations at the same time on the dependent variable. In other words, two
treatments can be simultaneously manipulated and their single and joint (known
as main and interaction) effects assessed. For example, the manager of the bus
company might be interested in knowing passenger increases if he used three
different types of buses (Luxury Express, Standard Express, Regular) and manip-
ulated both the fare reduction and the type of vehicle used, simultaneously. Fig-
ure 7.11 illustrates the 3 × 3 factorial design that will be used for the purpose.
Here, two factors are used with three levels of each. The above is completely
randomized, since the fares are randomly assigned to one of nine treatment com-
binations. A wealth of information can be obtained from this design. For exam-
ple, the bus company manager would know the increase in passengers for each
fare reduction, for each type of vehicle, and for the two in combination. Thus,
the main effects of the two independent variables as well as the interactions
among them can be assessed. For this reason, the factorial design is more effi-
cient than several single-factor randomized designs.
It is also statistically possible to control one or more variables through covari-
ance analysis. For example, it may be suspected that even after randomly
assigning members to treatments, there is a further “nuisance” factor. It is possi-
ble to statistically block such factors while analyzing the data.
Several other complex experimental designs are also available and are treated
in books devoted to experimental designs.