1. CHAPTER 13: THE NUTS AND BOLTS OF QUASI- EXPERIMENTS

2. 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. Quasi-experiment/subject variable: variable that allows comparison of groups of participants without manipulation (i.e., no random assignment). McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

3. Quasi-Experiments Many applied studies that examine realistic behaviors make use of quasi-experiments because random assignment would be difficult or impossible or unethical. For example, research done in educational settings often involves a quasi-experiment, because the researcher cannot affect the classroom students are in or the teacher they have. Thus, different classes of students may be compared with other factors than the one of interest changing across the classes due to the lack of random assignment. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

4. Pretest-Posttest Designs A behavior is measured twice: once before a treatment or condition is implemented (the pretest) and once after it has been implemented (the posttest). This design is a quasi-experiment because there is no random assignment of participants to the treatment. In this case, all the participants get the treatment. The researcher compares the scores from the pretest and the posttest, looking for a change based on the treatment or condition occurring between the two measurements. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

5. Pretest-Posttest Designs McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

6. Pretest-Posttest Designs Researchers can attempt to deal with some of the alternative explanations in pretest-posttest designs by including a control group. If participants are randomly assigned to the control group and the treatment group, the study becomes an experiment. However, in many situations random assignment to groups may not be possible. Without random assignment, the study is still a quasi-experiment, where it is difficult to rule out alternative explanations of the results. This design is a pretest-posttest design with nonequivalent groups, because group differences that might account for the results are not controlled by random assignment to groups. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

7. Pretest-Posttest Designs Sources of bias  History effects  events that occur during the course of a study to all or individual participants that can result in bias.  Example: A study was reported in the media during the time between measurements of smoking cessation that concluded that smoking has extremely harmful effects. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

8. Pretest-Posttest Designs Sources of bias  Testing effects  occur when participants are tested multiple times and each subsequent test is affected by the previous tests.  Example: participants may get better on the tests over time with practice. Alternatively, they may become fatigued or bored with the test after taking it once. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

9. Pretest-Posttest Designs Sources of bias  Regression toward the mean  can occur when participants score higher or lower than their personal average—the next time they are tested, they are more likely to score near their personal average, making scores unreliable.  Example: A high score achieved at posttest may be an extreme score in some cases, and with additional testing, these students may score closer to their original mean (which is typically lower than the norm). McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

10. Pretest-Posttest Designs One method of evaluating testing effects in pretest- posttest studies is the use of the Solomon four-group design (Shadish et al., 2002). In the Solomon four-group design, the pretest-posttest design with nonequivalent groups is used. However, two sets of each group type are included: one set that takes the pretest and posttest and one set that takes only the posttest to allow comparison of the two sets of groups. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

11. Time-Series Designs Time-series designs are special pretest-posttest designs that account for these fluctuations by measuring the behavior or attitude multiple times before the treatment and multiple times after the treatment over the same time period. Then the patterns of scores over time before and after the treatment are compared to determine if a difference has occurred. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

12. Time-Series Designs Interrupted time-series design  a time-series design where the “treatment” is an independent event, such as a historical event. Events such as a war, passage of a new law, or other historical events are considered “treatments” in an interrupted time-series design in that patterns of scores are compared before and after the event occurs. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

13. Time-Series Designs Noninterrupted time-series design  a time-series design where the “treatment” is implemented by the researcher. Suppose a researcher was interested in the effect of a new therapy on depression. The researcher may choose to conduct an interrupted time-series design in this case because depressive symptoms may change throughout the year. Thus, in a noninterrupted time-series design in this case, the participants’ depression symptoms would be measured over a period of time before they began the new therapy. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

14. Time-Series Designs As with pretest-posttest designs, limitations of time series designs exist due to possible extraneous factors that may affect a score pattern change other than the treatment or event of interest. Researchers must be cautious in interpreting relationships found between the treatment or event and the results, as with all quasi-experiments. Due to the focus on patterns of scores over time, traditional data analysis techniques are typically inadequate to testing hypotheses for these types of designs. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

15. Sources of Bias in Quasi-Experiments History  events that occur during the course of a study to all or individual participants that can result in bias. Example  Suppose that during the time a depression study was being conducted, the economy took a turn for the worse and many people were losing their jobs and having difficulty paying bills. In this case, the historical event (the economy declining) could affect the depression levels of participants in the study, making it difficult to detect positive effects of the treatments being tested. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

16. Sources of Bias in Quasi-Experiments History  events that occur during the course of a study to all or individual participants that can result in bias. Example  Suppose that during the time a depression study was being conducted, the economy took a turn for the worse and many people were losing their jobs and having difficulty paying bills. In this case, the historical event (the economy declining) could affect the depression levels of participants in the study, making it difficult to detect positive effects of the treatments being tested. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

17. Sources of Bias in Quasi-Experiments Maturation  natural changes that occur to the participants during the course of a study that can result in bias. Example  this can include actual maturation, as in developmental studies where individuals are observed at different ages, or other types of changes that occur to individuals over a period of time. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.

18. Sources of Bias in Quasi-Experiments Attrition  occurs when participants choose not to complete a study. Example  in the depression treatment study, suppose that some of the participants in the study drop out during the 12-week period and do not return for the posttest. It is possible that these participants who have chosen not to complete the study did so because they have worse depression symptoms than the participants that remained in the study. McBride, The Process of Research in Psychology. Third Edition © 2016 SAGE Publications, Inc.