1. The Nuts and Bolts of Quasi-Experiments
Chapter 12
The Nuts and Bolts of
Quasi-Experiments
Dawn M. McBride
The Process of Research in Psychology
Second Edition

2. Steps in the Research Process
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

3. Quasi-Experiments
A type of research design where a comparison is made, as in an experiment, but no random assignment of participants to groups occurs
Pretest-Posttest designs
Time series designs
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

4. Quasi-Experiments
Behaviors fore which random assignment would be difficult, impossible or unethical.
Field settings: Schools, mental health agencies
Parenting behaviors
Quality of Therapists
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

5. Pretest-Posttest Designs
No control group: compare post-test with pre-test scores
May include control group, without random assignment: non-equivalent groups
Implement a new intervention with one classroom of 8th graders and use another classroom as control
If random assignment is used– then study is an experiment (pre-test may be used or not)
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

6. Pretest-Posttest Designs
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

7. Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

8. Sources of bias: History effects- Regression towards the mean
events that occur during the course of a study to all or individual participants that can result in bias.
9-11
Hurricane
Regression towards the mean
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

9. Pretest-Posttest Designs: Bias
Testing effects
Possible solution
Solomon four-group design (Shadish et al., 2002).
one set takes the pretest and posttest
one set that takes only the posttest
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

10. Pretest-Posttest Designs
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

11. Time Series Designs
Measuring the behavior or attitude multiple times before and event or ttreatment and multiple times after over the same time period.
The patterns of scores over time before and after the event or treatment are compared to determine if a difference has occurred.
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

12. Time Series Designs: Interrupted
The “treatment” is an independent event, such as a historical event.
Iraq war
Patterns of scores are compared over time: before and after the event occurs
Typically uses archival data: e.g. Consumer confidence Index; Census Data
Requires sophisticated data analyses procedures
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

13. FDA warning Oct 2013 antidepressants and suicide risk
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

14. Noninterrupted Time Series Designs
The “treatment” is implemented by the researcher
The participants’ depression symptoms would be measured over a period of time
before they began the new therapy
after therapy concludes
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

15. Noninterrupted Time Series Design
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.

16. Times Series D. Sources of Bias
History
recession, natural events
Maturation
changes that occur to the participants during the course of a study that can result in bias
Developmental changes
Attrition
Dawn M. McBride - The Process of Research in Psychology, 2nd Edition © 2013 SAGE Publications, Inc.