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Chapter 8

PSYC 2030 Chapter Notes - Chapter 8: Environmental Factor, Analysis Of Variance, Factorial Experiment


Department
Psychology
Course Code
PSYC 2030
Professor
Rebecca Jubis
Chapter
8

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Chapter 8: Experimental Design II - Factorial Designs
Factorial Essentials
A factorial design involves any study with more than one independent variable (the
terms “independent variable” and “factor” mean the same thing) factorial designs could
have many independent variables but in practice these designs involve two or three
factors, sometimes four.
Identifying Factorial Designs
A factorial is described with a numbering system that identifies the number of
independent variables and the number of levels of each variable, for example, 2 X 3
factorial design has two independent variables the first has two levels and the second
has three OR a 3 X 4 X 5 factorial design has three independent variables, with three,
four and five levels.
The total number of conditions to be tested in a factorial study can be identified by
looking at all possible combinations of the different levels of each independent variable
which produces a factorial matrix the term “levels” refers to the number of levels of
the independent variable whereas the term “conditions” equals the number of cells in a
matric, for example, the 2 X 2 memory study has two independent variables, each with
two levels and it has four different conditions because of the four cells in the matrix the
number of conditions can be determined by calculating the product of the numbers in the
notation system, for example, 3 X 3 design has nine conditions and 2 X 2 X 2 design has
eight conditions.
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Outcomes Main Effects and Interactions
In factorial studies/designs, two kinds of results occur main effects and interactions.
Main effects refer to the overall influence of the independent variables, and interactions
examine whether the variables combine to form a more complex result.
Main Effects
In the memory study, the researcher is interested in the effects of two independent
variables: type of training and presentation rate the term main effect is used to describe
the overall effect of a single independent variable therefore, in a study with two
independent variables, 2 X 2 factorial, there can be at most two significant main effects.
Determining the main effect of one variable or factor involves combining all of the data
for each of the levels of that factor in the memory study, the main effect of type of
training is determined by combining the data for those trained to use imagery (for both
presentation rates) and comparing it to all of the data for those using rote repetition.
The way to find out if there is a main effect of type of training is to compare all of the
“imagery” data with all of the “rote” data – this involves calculating what are called row
means and you would calculate column means in order to see if there is a main effect of
presentation rate you would have to conduct ANOVA to see if the differences are
statistically significant or simply due to chance.
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