2. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Chapter 14 Single-n Designs and Quasi-Experiments

3. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Overview l Inferring causality in randomized experiments l Single-n designs l Quasi-experiments

4. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Inferring Causality in Randomized Experiments l Establishing covariation: Differences between treatment conditions l Establishing temporal precedence: IV before DV l Battling spuriousness: Statistics accounting for random variation

5. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Single-n Designs l Keeping nontreatment factors constant: The A-B design l Variations on the A-B design l Evaluation of single-n designs l Conclusions about single-n designs

6. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley The A-B Design l Stable baseline necessary, can still be tripped up by –Maturation –Testing

7. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley The A-B-A Design l Return to baseline would be nice, but may not occur because of –Maturation –Testing –Carryover

8. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Psychophysical Designs l One of first designs used in psychology l Present stimuli many times in many different randomized or counterbalanced sequences to balance out order effects

9. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Multiple-baseline design l Often used in operant conditioning studies l Collect baselines for several behaviors l Reinforce one of the behaviors. See if that behavior increases (and the others don’t) l Reinforce a second behavior…

10. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Evaluation of Single-n Designs l Internal validity may be threatened by maturation or testing l Construct validity may be damaged by sensitization l External validity may be better than you might first think –Replication –Study of fundamental processes l Ideally suited for some applied problems

11. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Quasi-Experiments l The problem: Accounting for nontreatment factors l Time-series designs l The nonequivalent control-group design l Conclusions about quasi-experimental designs

12. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley The Problem: Accounting for Nontreatment Factors l Step 1: Identify them l Step 2: Rule them out

13. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Identifying the Spurious 8 l Individuals changing without treatment 1. Maturation 2. History 3. Testing l Measurement error disguised as a treatment effect 4. Instrumentation 5. Regression

14. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Identifying the Spurious 8 (cont) l Non-treatment differences between groups 6. Mortality 7. Selection 8. Selection by maturation interactions

15. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Ruling out the Spurious 8 l Find out what threats are automatically ruled out by your design l Use logic to try to rule out the remaining threats

16. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Time-Series Designs l An extension of the pretest-posttest design l Selection, selection by maturation automatically eliminated

17. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Time-Series Designs (cont) l Baseline data allows one to estimate the effect of other threats. Changes greater than those expected by baseline data may be due to treatment. l Problem: Participants may change more than baseline data may suggest because of –History! –Regression –An inconsistent mortality, maturation, testing, or instrumentation effect

18. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Variations on the Traditional Time-Series Design l Reversal time-series design l Two-group time-series design. “Control group” may be able to rule out some history effects

19. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley The Nonequivalent Control- Group Design l Selection is a serious problem l Matching doesn’t eliminate selection problems because can’t perfectly match on all relevant variables l Matching may lead to other problems, such as: –Regression effects –Selection X maturation interactions

20. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Conclusions about Quasi- Experimental Designs l More flexible than experimental designs l Less internal validity than experimental designs l Researcher can take steps to eliminate a threat that isn’t automatically eliminated by the design l Often, a threat can’t be eliminated. In that case, the researcher may argue that the treatment is a more likely explanation for the effect than the threat. This argument may be based on the law of parsimony

21. PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Concluding Remarks l If you can’t do an experiment, single-n and quasi-experiments may be viable alternatives l If you don’t want to make cause-effect statements, you shouldn’t use experiments, single-n designs, or quasi-experiments