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

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

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

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

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

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

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

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…

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

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

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

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

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

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

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

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

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

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

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

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