factorial designs 03
TRANSCRIPT
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Outline
1. Introduction to factorial designs2. Main effects and interactions3. Types of factorial designs
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1. Introduction to factorial designs
in real life variables rarely exist in isolation to examine these more complex, real-life
situations, researchers often designresearch studies that include more thanone independent variable (e.g. caffeine
and alcohol)
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1. Introduction to factorial designs
in an experiment, an independent variable isoften called a factor, especially in experimentsthat include two or more independent variables
a research design that includes two or morefactors is called a factorial design
this kind of design is often referred to by thenumber of its factors, as a two-factor design ora three-factor design
a research study with only one independentvariable is often called a single-factor design
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1. Introduction to factorial designs
each factor is usually denoted by a letter (A, B,C)
factorial designs use a notation system thatidentifies both the number of factors and thenumber of values or levels that exist for eachfactor
e.g. caffeine (3 levels) and alcohol study (2levels) would be described as 3 x 2 two factordesign
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2. Main effects and interactions
the main differences among the levels of onefactor are called the main effect of that factor
when the research study is represented as amatrix with one factor defining rows and thesecond factor defining the columns, then themean differences among the rows define the
main effect for one factor, an the meandifferences among the columns define the maineffect for the second factor
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2. Main effects and interactions
an interaction between factors occurs whenever themean differences between individual treatmentconditions, or cells, are different from what is predicted
from the overall main effect of the factors when the effects of one factor depend on the differentlevels of a second factor, then there is an interactionbetween the factors
when the results of a two-factor study are graphed, theexistence of nonparallel lines (lines that cross orconverge) is an indication of an interaction between thetwo factors
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Main effects of caffeine and alcoholno interaction
alcohol and caffeine no interaction
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caffeine
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alcohol
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Main effects of caffeine and alcoholinteraction
alcohol and caffeine interaction
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caffeine
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alcohol
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3. Types of factorial designs
between-subjects designs there is a separate group of participants for
each of the treatment conditions large number of participants e.g. 20participants in each condition for a 2 x 4design means 160 participants
within-subjects designs single group of individuals participates in all of
the separate treatment conditions only 20 participants for 2 x 4 factorial design
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3. Types of factorial designs
mixed-designs (with respect to factors) between subjects design can apply to one factor and
a within-subjects design is preferable for a secondfactor (e.g. mood as between subjects factor andmemory as within subjects factor)
- a factorial study that combines two different researchdesigns is called a mixed design
- a common example of a mixed design is a factorialstudy with one between-subjects factor and onewithin-subjects factor
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3. Types of factorial designs
Experimental and nonexperimental orquasi-experimental research strategies
a factorial study that combines two differentresearch strategies a common example of a mixed design is a
factorial study with one experimental factor
and one nonexperimental factor (e.g. genderdifferences in memory tests)
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3. Types of factorial designs
Pretest-posttest control group designs Quasi-experimental (two factor mixed design)
One factor between subjects
treatment type Second factor within subjects pre-post testO X O (treatment group)O O (control group)
Experimental version of the same designR O X OR O OWhere R symbolizes random assignment of subjects
into groups
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3. Types of factorial designs
Higher-order factorial designs Complex designs involving three or more
factors Example of a three factor design examiningtwo teaching methods (A), boys and girls (B)and first and second grade classes (C)
This three factor design can be summarizedas 2x2x2 2 (two teaching methods) x 2 (boys and girls)
x 2 (first and second grade)