1. Chapter 12
Quasi-Experimental Research: A Close Cousin to Experimental Research

2. CHAPTER OBJECTIVES - STUDENTS SHOULD BE ABLE TO:
Identify and summarize examples of quasi-experimental design.
Discuss the differences between quasi-experimental, pre-experimental and true experimental designs.
List and explain the threats to validity common to quasi-experimental designs.
Explain how quasi-experimental designs differ from one another.

3. CHAPTER OBJECTIVES - STUDENTS SHOULD BE ABLE TO:
List and provide examples of the kinds of questions answered by developmental research.
Identify and explain the use of single-subject designs in experiments.
Discuss the advantages and disadvantages of longitudinal and cross-sectional methods.
Identify and explain the utility of follow-up studies.
Explain the importance of age in developmental research.

4. CHAPTER OVERVIEW The Quasi-Experimental Method
Quasi-Experimental Designs
Developmental Research

5. THE QUASI-EXPERIMENTAL METHOD

6. THE QUASI-EXPERIMENTAL METHOD
No control over group assignment
Useful when manipulation of variables is ethically, morally, or practically difficult

7. THE QUASI-EXPERIMENTAL METHOD
Quasi-experimental research is post hoc research
Internal validity is intermediate between pre-experimental and true experimental designs

8. QUASI-EXPERIMENTAL DESIGNS

9. THE NONEQUIVALENT CONTROL GROUP DESIGN
Participants Assigned to the Experimental Group
Pretest
Treatment
Post-test
Participants Assigned to the Control Group
No Treatment
Commonly used when random assignment is not possible
Similar to pretest post-test control group design
Selection bias is a threat to validity

10. THE STATIC GROUP COMPARISON
Experimental Group
Treatment
Post-test
Control Group
No Treatment
No pretest
Disadvantages
Questionable internal validity
Questionable external validity

11. SINGLE SUBJECT DESIGN
Measure Behavior During Baseline
Treatment
Remove Treatment—Measure Behavior During Reversal
Looks at cause and effect relationships in single individuals rather than in groups
Common in behavioral analysis and special education
Based on behavioral view of development

12. Measure Behavior During Baseline Treatment
Remove Treatment—Measure Behavior During Reversal

13. SINGLE SUBJECT DESIGN (Continued)
AB designs (simple single subject) measure baseline and impose treatment
ABA designs (reversal) remove treatment
ABAB (alternating treatment designs) re-impose treatment

14. MULTIPLE BASELINE DESIGNS
A variation of ABA design
Two behaviors, subjects, or occasions are focus of study
One receives treatment
Other serves as baseline “control”

15. EVALUATING SINGLE SUBJECT DESIGNS
Most have good internal validity
External validity may be questionable

16. DEVELOPMENTAL RESEARCH

17. THE LONGITUDINAL METHOD
Year of
Testing
1960
1965
1970
1975
1980
1940 20 25 30 35 40
1935 45 Of
1930 50
Birth
1925 55
1920 60
Age at
Testing
Assesses behavior in one group of people at several points in time
Examines age changes over an extended period of time

18. THE LONGITUDINAL METHOD
Advantages
Can study development over extended time period
Subjects are their own controls
Can study continuity between different groups
Some ability to infer cause and effect
Disadvantages
Expense
Mortality—people leave experiment

19. THE CROSS-SECTIONAL METHOD
Year of
Testing
1960
1965
1970
1975
1980
1940 20 25 30 35 40
1935 45 Of
1930 50
Birth
1925 55
1920 60
Age at Testing
Assesses behavior in several groups at one point in time
Examines age differences

20. THE CROSS-SECTIONAL METHOD
Advantages
Less expensive than longitudinal
Short time span
Mortality is minimized
Requires little cooperation between researchers and participants
Disadvantages
Groups are not strictly comparable
Little directional predictability
People of same age may be at different maturation levels
No ability to examine continuity of developmental processes

21. THE UTILITY OF FOLLOW-UP STUDIES
Data that have already been collected
Guide current and future research
Enable longitudinal research to be done in a short time

22. THE ROLE OF AGE IN STUDYING DEVELOPMENT
Age has a descriptive, not explanatory value
New research techniques consider:
Measurement effects—time of testing
Cohort effects—time of birth

23. CONFOUNDING OCCURS WHEN MULTIPLE VARIABLES CAN EXPLAIN THE SAME PHENOMENON
Year Of
Testing
1985
1990
1995
2000
2005 5 10 15 25
1980 20
Birth
1975 30
Sesame
Street
Debuted
Cross-sectional study of language skills
Test in 1995
Cohorts
Subjects aged 15 & 20 born before debut
Subjects aged 5 & 10 born after debut
Cohort and age are confounded

24. HAVE WE MET THE OBJECTIVES? CAN YOU:
Identify and summarize examples of quasi-experimental design?
Discuss the differences between quasi-experimental, pre-experimental and true experimental designs?
List and explain the threats to validity common to quasi-experimental designs?
Explain how quasi-experimental designs differ from one another?

25. HAVE WE MET THE OBJECTIVES? CAN YOU:
List and provide examples of the kinds of questions answered by developmental research?
Identify and explain the use of single-subject designs in experiments?
Discuss the advantages and disadvantages of longitudinal and cross-sectional methods?
Identify and explain the utility of follow-up studies?
Explain the importance of age in developmental research?