Chapter 9
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The differences between Between-Subjects (Bet-Ss) and Within-Subjects (W/in-Ss) designs in experimental psychology. the advantages and disadvantages of each design, threats to internal and external validity, and examples of studies using these designs. It also includes a discussion on how to replicate a study using a Within-Subjects design.
Typology: Lecture notes
2021/2022
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Between-subject design (Bet-Ss)
aka “Between-participant design” Experimental design and vocabulary Threats to internal validity Threats to external validity
Within-subject design (W/in-Ss)
aka “Correlated-groups designs” Within-participants design or “Repeated measures design” ▪ Participants complete all (2+) conditions. ▪ Researcher examines if difference between means ▪ e.g. pre-post-test, longitudinal study (vs. cross-sectional) ▪ Multiple testing sessions or complete conditions successively Matched-participants design
If Bower, Karlin, & Dueck was replicated using a
within-subject design, what would it look like?
What is the independent variable (IV)?
What are the levels of the IV?
What is the dependent variable (DV)?
What is measured?
Bet-Ss desgin W/in-Ss design
Ss Group Accuracy 1 no label 50 2 label 90 3 no label 60 4 label 85 5 no label 45 6 label 75 7 no label 30 8 label 90
Ss Acc-Label Acc-NoLabel 1 90 50 2 85 60 3 75 45 4 90 30
MORE data from fewer Ss!!
Duke undergraduates
tested day after 9/
(Flashbulb memory - FB)
Tested again at 1, 6, or 32
weeks after 9/
DV: consistency of FB
and everyday memory
Results:
Both types of memory declined over time No relationship between accuracy and confidence in memory
Method
IV: group (training vs. no training)
IV: Training - 12+ days on working memory task
“n-back” http://brainworkshop.sourceforge.net/
DV: Performance on intelligence task before and after
training sessions
PRO
Need fewer Ss (compared to bet-Ss) Or get more data! Can take less time If all conditions are in 1 session rather than separate sessions for each Ss Increases POWER Decreases variability Less individual differences so more likely effect is due to IV not b/c Ss in grps are different
CON Testing effects Fatigue effect Practice effect Order effect Carry-over effects (“transfer”) 1 st^ condition affects performance in 2nd^ condition e.g. knowledge, attitude, etc. Increase in demand characteristics aka “participant effects” Ss has more info about the study so can change behavior
Distribute potential order effects evenly over groups by
using counterbalancing techniques
If use w/in-Ss design for Bower, Karlin & Dueck
½ Ss receive label then no-label condition ½ Ss receive no label then label condition
Complete counterbalancing
If 4 conditions = 24 possible orders!
Partial counterbalancing
Randomly select orders to use
Latin squares design
Same # orders as # of conditions Each condition presented at each order
E.g. 3 conditions: ABC / BCA / CAB
Use separate groups of Ss for each condition
BUT, Ss for each condition are similar
What variables should Ss be matched on?
How many variables should Ss be matched on?
It depends on the study!
Used (more often) in clinical or drug research
Match based on:
Person variables (gender, age, ethnicity)
Others such as intelligence, socioeconomic status
Can also use “natural pairs” such as twins
Ss fill-out “test of
language ability”
Unknowingly “primed”
w/ stereotypes of words
in 1 of 3 categories
Examine how quickly Ss
interrupts conversation
of experimenter w/ friend
College students rate
pronounceability of
famous and non-
famous male and
female names
Later (24hrs/48hrs)
judged whether each
name was famous or
not
50
55
60
65
70
75
80
Familiar M Familiar F Unfamiliar M Unfamiliar F
Percent hits
Male Female
74% 65% 68% 61%
0
2
4
6
8
10
Familiar M Familiar F Unfamiliar M Unfamiliar F
Percent false alarms
Nonequivalent control grp
Use random assignment Use pretest/posttest design
History
Test at different time pts
Maturation
Use control group
Testing effect
Use control group
Regression to mean
Use control grp w/ same extreme scores
Instrumentation effect
Use control group
Mortality or attrition
Use control group
Diffusion of treatment
Tell Ss not to discuss study
Experimenter or
participant effects
Use single-blind or double- blind method Use placebo group
Ceiling and floor effects
Carefully select DV to avoid