Non-experimental
Designs
Psyc 231: Research Methods
Non-experimental Designs
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Surveys
Developmental Designs
Small N Designs
Quasi-experiments
Developmental Designs
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Used to study development or changes in
behavior
Describe relationship between age and other
variables
Three main types
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Cross-sectional
Longitudinal
Cohort-sequential
Cross-sectional Designs
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Uses a separate group of participants for
each age group being compared
Different groups measured once and
compared to each other
Between subjects design
Most commonly used
Cross-sectional Designs
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Study the development
of memory over time
All three age groups
tested at one point in
time
Age 4
Age 7
Age 11
Cross-sectional Designs
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Advantages
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Short period of time
No real commitment
Gather all data at one time
Cross-sectional Designs
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Disadvantages
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Cohort/Generation effects
Does not tell real development of individual
Cannot infer causality
Longitudinal Designs
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Same participants are observed over time
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Assesses stability of traits
Individuals are compared to self throughout
repeated measures over time
Within subjects design
Longitudinal Designs
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Study of the
development of
memory over time
Same participants
tested over time
Age 4
Age 7
Age 11
Longitudinal Designs
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Advantages
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No generation effects
Examine individual differences
Can see developmental changes
Longitudinal Designs
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Disadvantages
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Very time consuming and costly
Hard to find patient participants – Subject
Attrition/Mortality
Researchers lose interest
Practice effects
Cross-generational effects
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Conclusions based on members of one generation
may not apply to other generations
Cannot determine causality
Longitudinal Designs
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Wisconsin Longitudinal Study (WLS)
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Began in 1957 and is still on-going (50 years)
Originally studied plans for college after
graduation
Now it can be used as a test of aging and
maturation
Cohort-sequential Designs
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Measure groups of participants as they age
Combines the best features of both
longitudinal and cross-sectional designs
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Studies specific age groups over time
Both between and within subjects design
Cohort-sequential Designs
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Study of the
development of
memory over
time
Test multiple
age groups
over time
Age 4
Age 8
Age 8
Age 12
Age 12
Age 16
Cohort-sequential Designs
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Advantages
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Saves time
Get more information
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Long-term effects and developmental changes
Compare to different ages
No generation effects
Cohort-sequential Designs
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Disadvantages
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More time consuming than cross-sectional
Does not mean causation
Small N Designs
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Study one or few participants (typically 3-8
participants)
Each individual is analyzed separately
Common type of design until 1920’s
Still used in some areas of research: clinical
settings, phenomenon
Different from case studies
Small N Designs
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Typically observe participants
Baseline studies
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Observation/testing generally occurs at 3 points
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Effect doesn’t occur before IV (baseline)
Show that effect occurs with IV (treatment)
Doesn’t occur without IV (reversibility)
Before treatment, after treatment, after reverse treatment
Examine level and trend to determine effect
Small N Designs
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Level
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How frequent or intense is the behavior?
Are the data points high or low?
Trend
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Does the behavior increase or decrease?
Are the data points flat or on a slope?
Small N Designs
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ABA design (baseline, treatment, baseline)
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A
Must be able to reverse effect
 Could not have been due to maturation, history, etc.
Effectiveness of a drug
B
A
Steady state (baseline) | Transition steady state | Reversibility
Small N Designs
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Advantages
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Focus on individual performance
Can see big effects
Avoid some ethical problems (nontreatments/controls)
Allows to look at unusual (and rare) types of
subjects
Often used to supplement large N studies, with
more observations on fewer subjects
Small N Designs
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Disadvantages
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Generalizability
Effects may be small relative to variability of
situation
Some effects are by definition between subjects
Treatment can lead to a lasting change, so you
don’t get reversals
Ethical issues with reversing treatment
Small N Designs
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Hermann Ebbinghaus
(1885) studied memory
of nonsense syllables
on himself
Discovered the
forgetting curve and
learning curve
Know a lot about
memory today because
of him
Quasi-experimental Designs
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Almost “true” experiments but lack of control
over assignment of participants
Independent variable cannot be manipulated
(inherent confound)
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Subject variable
Time could be variable (Developmental)
Random variable already present
Quasi-experimental Designs
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Advantages
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Allows applied research when experiments not
possible
Threats to internal validity can (sometimes) be
assessed
Practical and more feasible than true
experiments, especially in clinical settings
Some generalizability
Quasi-experimental Designs
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Disadvantages
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Difficult to make clear cause-and-effect
statements
Statistical analysis can be difficult
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Most statistical analyses assume randomness
Can not randomize assignment to groups
Quasi-experimental Designs
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Common types
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Non-equivalent control groups design
Time series designs
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Interrupted time series design
Control group interrupted time series design
Quasi-experimental Designs
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Non-equivalent control groups design
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Typically used as a pretest-posttest
Assignment based on already established
variable
Between subjects design
Non-Random
Assignment
Dependent
Variable
Measure
Independent
Variable
Experimental
group
Dependent
Variable
Measure
participants
Measure
Control
group
Measure
Quasi-experimental Designs
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Non-equivalent control groups design:
Pretest-posttest
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Example
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Individuals high on self-esteem and low on selfesteem
Pretested on depression levels
Intervention given to low self-esteem group
Posttested on depression levels
Quasi-experimental Designs
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Time series designs
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Interrupted times series design
 Observe on several occasions before and after the
independent variable occurs
 Within subjects design
obs obs obs Treatment obs obs obs
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The pretest observations allow the researcher to look for
pre-existing trends
The posttest observations allow the researcher to look for
changes in the trends
Quasi-experimental Designs
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Time series designs
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Control group interrupted time series design
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A variation of the interrupted time series designs
Series of observations followed by treatment for
experimental condition
Compared to a control group
obs obs obs Treatment obs obs obs
obs obs obs
obs obs obs
Questions?