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

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.

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.

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

THE QUASI-EXPERIMENTAL METHOD

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

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

QUASI-EXPERIMENTAL DESIGNS

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

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

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

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

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

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”

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

DEVELOPMENTAL RESEARCH

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

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

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

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

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

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

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

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?

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?