1. Non-experimental Designs
Psyc 231: Research Methods

2. Non-experimental Designs
Surveys
Developmental Designs
Small N Designs
Quasi-experiments

3. Developmental Designs
Used to study development or changes in behavior
Describe relationship between age and other variables
Three main types
Cross-sectional
Longitudinal
Cohort-sequential

4. Cross-sectional Designs
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

5. Cross-sectional Designs
Study the development of memory over time
All three age groups tested at one point in time
Age 4
Age 7
Age 11

6. Cross-sectional Designs
Advantages
Short period of time
No real commitment
Gather all data at one time

7. Cross-sectional Designs
Disadvantages
Cohort/Generation effects
Does not tell real development of individual
Cannot infer causality

8. Longitudinal Designs Same participants are observed over time
Assesses stability of traits
Individuals are compared to self throughout repeated measures over time
Within subjects design

9. Longitudinal Designs Study of the development of memory over time
Same participants tested over time
Age 4
Age 7
Age 11

10. Longitudinal Designs Advantages No generation effects
Examine individual differences
Can see developmental changes

11. Longitudinal Designs Disadvantages Very time consuming and costly
Hard to find patient participants – Subject Attrition/Mortality
Researchers lose interest
Practice effects
Cross-generational effects
Conclusions based on members of one generation may not apply to other generations
Cannot determine causality

12. Longitudinal Designs Wisconsin Longitudinal Study (WLS)
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

13. Cohort-sequential Designs
Measure groups of participants as they age
Combines the best features of both longitudinal and cross-sectional designs
Studies specific age groups over time
Both between and within subjects design

14. Cohort-sequential Designs
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

15. Cohort-sequential Designs
Advantages
Saves time
Get more information
Long-term effects and developmental changes
Compare to different ages
No generation effects

16. Cohort-sequential Designs
Disadvantages
More time consuming than cross-sectional
Does not mean causation

17. Small N Designs
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

18. Small N Designs Typically observe participants Baseline studies
Effect doesn’t occur before IV (baseline)
Show that effect occurs with IV (treatment)
Doesn’t occur without IV (reversibility)
Observation/testing generally occurs at 3 points
Before treatment, after treatment, after reverse treatment
Examine level and trend to determine effect

19. Small N Designs Level Trend How frequent or intense is the behavior?
Are the data points high or low?
Trend
Does the behavior increase or decrease?
Are the data points flat or on a slope?

20. Small N Designs ABA design (baseline, treatment, baseline)
Must be able to reverse effect
Could not have been due to maturation, history, etc.
Effectiveness of a drug

21. Small N Designs Advantages Focus on individual performance
Can see big effects
Avoid some ethical problems (non-treatments/controls)
Allows to look at unusual (and rare) types of subjects
Often used to supplement large N studies, with more observations on fewer subjects

22. Small N Designs Disadvantages 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

23. Small N Designs
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

24. Quasi-experimental Designs
Almost “true” experiments but lack of control over assignment of participants
Independent variable cannot be manipulated (inherent confound)
Subject variable
Time could be variable (Developmental)
Random variable already present

25. Quasi-experimental Design s
Advantages
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

26. Quasi-experimental Designs
Disadvantages
Difficult to make clear cause-and-effect statements
Statistical analysis can be difficult
Most statistical analyses assume randomness
Can not randomize assignment to groups

27. Quasi-experimental Designs
Common types
Non-equivalent control groups design
Time series designs
Interrupted time series design
Control group interrupted time series design

28. Quasi-experimental Designs
Non-equivalent control groups design
Typically used as a pretest-posttest
Assignment based on already established variable
Between subjects design
participants
Experimental
group
Control
Measure
Non-Random
Assignment
Independent Variable
Dependent Variable

29. Quasi-experimental Designs
Non-equivalent control groups design: Pretest-posttest
Example
Individuals high on self-esteem and low on self-esteem
Pretested on depression levels
Intervention given to low self-esteem group
Posttested on depression levels

30. Quasi-experimental Designs
Time series designs
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
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

31. Quasi-experimental Designs
Time series designs
Control group interrupted time series design
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

32. Questions?