© 2011 pearson prentice hall, salkind. quasi- experimental research: a close cousin to experimental...
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© 2011 Pearson Prentice Hall, Salkind.
Quasi-Experimental Research: A Close Cousin to Experimental Research
© 2011 Pearson Prentice Hall, Salkind.
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.
© 2011 Pearson Prentice Hall, Salkind.
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.
© 2011 Pearson Prentice Hall, Salkind.
The Quasi-Experimental Method
Quasi-Experimental Designs
Developmental Research
© 2011 Pearson Prentice Hall, Salkind.
© 2011 Pearson Prentice Hall, Salkind.
No control over group assignment
Useful when manipulation of variables is ethically, morally, or practically difficult
© 2011 Pearson Prentice Hall, Salkind.
Quasi-experimental research is post hoc research
Internal validity is intermediate between pre-experimental and true experimental designs
© 2011 Pearson Prentice Hall, Salkind.
© 2011 Pearson Prentice Hall, Salkind.
Commonly used when random assignment is not possible
Similar to pretest post-test control group design
Selection bias is a threat to validity
Participants Assigned to the Experimental Group
Pretest Treatment Post-test
Participants Assigned to the Control Group
Pretest No Treatment Post-test
© 2011 Pearson Prentice Hall, Salkind.
No pretest
Disadvantages◦ Questionable internal validity◦ Questionable external validity
Experimental Group Treatment Post-test
Control Group No Treatment Post-test
© 2011 Pearson Prentice Hall, Salkind.
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
Measure Behavior During
BaselineTreatment
Remove Treatment—Measure Behavior During Reversal
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Measure Behavior During Baseline
TreatmentRemove Treatment—Measure
Behavior During Reversal
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AB designs (simple single subject) measure baseline and impose treatment
ABA designs (reversal) remove treatment ABAB (alternating treatment designs)
re-impose treatment
SINGLE SUBJECT DESIGN (Continued)
© 2011 Pearson Prentice Hall, Salkind.
A variation of ABA design
Two behaviors, subjects, or occasions are focus of study◦ One receives treatment◦ Other serves as baseline “control”
© 2011 Pearson Prentice Hall, Salkind.
Most have good internal validity
External validity may be questionable
© 2011 Pearson Prentice Hall, Salkind.
© 2011 Pearson Prentice Hall, Salkind.
Assesses behavior in one group of people at several points in time
Examines age changes over an extended period of time
Year of Testing
1960 1965 1970 1975 1980
1940 20 25 30 35 40
Year 1935 25 30 35 40 45
Of 1930 30 35 40 45 50
Birth 1925 35 40 45 50 55
1920 40 45 50 55 60
Age at
Testing
© 2011 Pearson Prentice Hall, Salkind.
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
© 2011 Pearson Prentice Hall, Salkind.
Assesses behavior in several groups at one point in time Examines age differences
Year of Testing
1960 1965 1970 1975 1980
1940 20 25 30 35 40
Year 1935 25 30 35 40 45
Of 1930 30 35 40 45 50
Birth 1925 35 40 45 50 55
1920 40 45 50 55 60
Age at Testing
© 2011 Pearson Prentice Hall, Salkind.
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
© 2011 Pearson Prentice Hall, Salkind.
Data that have already been collected◦ Guide current and future research
◦ Enable longitudinal research to be done in a short time
© 2011 Pearson Prentice Hall, Salkind.
Age has a descriptive, not explanatory value
New research techniques consider:◦ Measurement effects—time of testing◦ Cohort effects—time of birth
© 2011 Pearson Prentice Hall, Salkind.
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
Sesame Street
Debuted
• CONFOUNDING OCCURS WHEN MULTIPLE VARIABLES CAN EXPLAIN THE SAME PHENOMENON
Year Of Testing
1985 1990 1995 2000 2005
1990 5 10 15
Year 1985 5 10 15 25
Of 1980 5 10 15 20 25
Birth 1975 10 15 20 25 30
© 2011 Pearson Prentice Hall, Salkind.
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?
© 2011 Pearson Prentice Hall, Salkind.
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?