CHAPTER OVERVIEW

• The Nonequivalent Control Group Design

• The Static Group Comparison • Single-Subject Design • Evaluating Single-Subject Designs

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

THE NONEQUIVALENT CONTROL GROUP DESIGN

• 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

THE STATIC GROUP COMPARISON

• No pretest• Disadvantages

– Questionable internal validity– Questionable external validity

Experimental Group

Treatment Post-test

Control Group No Treatment Post-test

SINGLE SUBJECT DESIGN

• 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

Measure Behavior

During BaselineTreatment

Remove Treatment—Measure Behavior During

Reversal

• AB designs (simple single subject) measure baseline and impose treatment

• ABA designs (reversal) remove treatment

• ABAB (alternating treatment designs) re-impose treatment

EVALUATING SINGLE SUBJECT DESIGNS

• Most have good internal validity• External validity may be

questionable