Chapter 11: Quazi-Experimental Designs

Single Participant Designs

Does an IV affect a single participant?: aka small-n designs

Reversal Designs (ABA): Did IV have the intended effect?

Reversal Designs

A single reversal not very impressive

Perhaps unethical

Multiple Baseline Designs

Avoids withdrawing a treatment

Across participants

Across behaviors

Across situations

Across Participants

Uses several participants

Introduces manipulation at different points

Across Behaviors

Uses several behaviors

Introduces manipulation at different points in time to the different behaviors

Punishment system = biting & grooming

Across Settings

Same behavior measured in different settings

Manipulation used in both settings at different points in time Program Evaluation

Needs Assessment

Program Theory Assessment

Process Evaluation

Outcome Evaluation

Efficiency Assessment

Quazi-Experimental Designs

Not true experimental designs

Provide experimental-like controls to minimize threats to internal validity

Missing Control Group Design (aka One-Group Post-test Only Design)

Group  Treatment  Post-test

One-Group Pretest-Post-test Design

Group  Pre  Treat  Post

1. Hyperactive children

2. Impose 4-week dietary restriction (Treatment)

3. Observe them again (Post-test)

Threats to Internal Validity

History: Any event occurring between the first and second measurement

Maturation: Processes within the participant due to the passage of time

Testing: The effects of taking a test twice

Instrumentation: Autonomous changes in the measuring instrument

Statistical Regression: Groups are selected on the basis of extreme scores

Selection: Differential selection of participants to groups Experimental Mortality: Loss of participants

Statistical Conclusion Validity: Assumptions of a test are violated

Non-Equivalent Control Group Designs

Non-Equivalent Control Group Pretest Post-test Design

Group A Group B   Pretest Pretest   Treatment No Treatment   Post-test Post-test

Interrupted Time Series Design

Measure the DV before and after some naturally occurring event

Event = Quazi-IV

O’Malley and Wagenaar (1991)

Raising drinking age results in fewer fatal accidents

loss of highway funding by 1986 26 states raised drinking age between 1976-1987 Results:

15% decrease for drivers under 21

5% decrease for drivers over 21

Control Series Design

Using a control group in an interruputed time series design

Developmental Research Designs

Cross-Sectional

Longitudinal

Sequential