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Advantages of Between-Subjects Designs
Includes a control or comparison group that helps to control for many extraneous variables.
Can randomly assign participants to groups, which helps to balance extraneous variables across the groups.
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Disadvantages of Between-Subjects Designs
You can’t always randomly assign participants to groups.
Large individual differences between participants may make it difficult to observe meaningful group differences.
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If the subjects are used more than once or matched, this design is called a
Within-Subjects Design
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Advantages of Within-Subjects Design
They take fewer participants.
They typically have more statistical power (such as a matched t-test)
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Disadvantages of Within-Subjects Design
You have to worry about practice effects and carryover effects
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equalizing the amount of practice, for example, you could test one person in the B1, B2, B3 order, another with B1, B3, B2, until every order is tested; used to avoid practice and carryover effects
counterbalancing
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a factorial design in which there is at least one between-subjects factor and at least one within-subjects design
mixed design
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Mixed Designs are useful when:
You might end up testing the subjects too much in a wholly within-subjects design
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total variance=
systematic + nonsystematic variance
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"between group" variance; experimental variance due to the IV; due to confounding variables
systematic variance
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error variance or variance within the groups; due to chance factors
nonsystematic variance
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If between-group variation is not significantly ______ than within-group variance, then group differences probably do not contribute anything beyond chance variability
greater
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statistical anaylsis comparing more than 2 sets of scores
ANOVA
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Sources of sequence/carryover effects
learning, fatigue, habituation, sensitization, contrast, adaptation
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ways to deal with carryover effect
random order; counterbalancing
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advantages of matched design
can control for subject variables that may otherwise obscure the effect of the IV
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disadvantages of matched design
matching variable needs to be reliable, difficult finding enough participants who are matched, impossible to match on every possible variable that might influence the IV
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when greater than 2 IV, we can examine _______ and ______
main effects; interactions
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overall effect of one IV (ignoring the other)
main effect
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effect of one IV depends on the level of a second IV
interaction effect
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