PSY3062 Lecture Notes - Lecture 5: Complement Factor B, Repeated Measures Design
25 Jun 2018
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PSY3062 Lecture 5
Why use a Factorial Design?
Sarafino (2005) gives four reasons:
1. Enhances external validity
-by not limiting the study to examining the influence of only one IV
on the DV, you can improve the generalizability of the study’s
findings
2. More efficient
-whilst factorial designs require more participants and resources
than a single factor study, compared to conducting several single
factor studies to thoroughly examine a particular DV, conducting
one factorial design will be more efficient and provide more
information
3. Can test for interactions between factors
- i.e., factorial designs can not only examine the effects of each IV on its
own, but also the combined effects of the IVs (the interaction between
the factors)
-Examples of combined effects (interactions):
- a) A factor enhances the effects of another factor
- b) A factor diminishes or eliminates the effects of another factor
- c) A factor has opposite effects in the presence of another factor
4. Can use to control systematic and non-systematic variance
–i.e., include participant characteristics such as age or gender as
independent variables and reduce the error variance of the analysis
(which will make the statistical analysis more powerful). Including
additional variables also enables you to test whether these variables are
acting as confounding variables.
Factorial means two or more factors (IVs)
Terminology:
–‘Two way’ means two factors
–‘Three way ’means three factors
–‘Four-way’ means four factors, and so on
These factors can be:
- Independent-measures (between-subjects)
- Repeated measures (within-subjects)
- Mixed-model- a combination of independent and repeated measures
factors (some between-subjects and within-subject)
How many levels of each factor?
-Use numerical code (e.g., 2 x 2) to designate the number of levels
of each factor
‘2x3_’means that there are 2 levels of Factor A, and 3 levels of Factor B.
Because there are two numbers, and therefore, two factors, it is a two-way
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