PSYC512: Research Methods Lecture 13

1. PSYC512: Research MethodsLecture 13 Brian P. Dyre University of Idaho PSYC512: Research Methods

2. Lecture 13 Outline • Review of Lectures 11-12 • Causation and reactivity • Within vs. between subjects designs • More on research design • Multifactor research – using two or more independent variables • An example of multi-factor research • Experimentation vs. Quasi-experimentation PSYC512: Research Methods

3. Factorial Research Designs • Used to assess the effects of 2 or more independent variables (factors) on your dependent variable • Using multiple IVs in one experiment is • more economical (particularly for within-Ss) • provides more information • Main effects of each IV (separate effects of each IV) • Interaction between the IVs (synergism): effect of one variable changes across the levels of the other variable PSYC512: Research Methods

4. Factorial Research Designs: Possible Outcomes of a 2 x2 Design No effects Main Effect A Only Main Effect B Only B1, B2 B2 DV DV DV B1, B2 B1 A1 A2 A1 A2 A1 A2 Factor A Factor A Factor A PSYC512: Research Methods

5. Factorial Research Designs: Possible Outcomes of a 2 x2 Design Main Effects for A and B, No Interaction Main Effects for A and B, Interaction (ordinal) Main Effect for A only, Interaction (disordinal) Main Effect for B only, Interaction (ordinal) B2 B2 B2 B2 B1 B1 DV DV DV DV B1 B1 A1 A2 A1 A2 A1 A2 A1 A2 Factor A Factor A Factor A Factor A IMPORTANT: always interpret the highest order effect or interaction PSYC512: Research Methods

6. Example Factorial Experiment: Perceiving Heading • An experiment on perceiving the heading direction during steering control vs. riding and pointing PSYC512: Research Methods

7. Example Factorial Experiment: Perceiving Heading • IV1: observer’s task • Steering control: Steer so that you appear to be moving straight ahead • Pointing: Point in the direction towards which you perceive yourself to be moving while “riding” • IV2: simulated velocity of observer movement • Three levels: 50, 100, and 200 ms-1 • Dependent Variable (measure): RMS (root-mean-squared) heading error = sqrt(Serror/N) PSYC512: Research Methods

8. Results • Significant Effects • Task Main Effect • Interaction between task and velocity • IMPORTANT! ALWAYS INTERPRET HIGHEST ORDER EFFECT PSYC512: Research Methods

9. Specialized Research Designs • Combining between-subjects and within-subjects factors in research design – mixed designs • Combining experimental and correlational designs (Analysis of covariance or ANCOVA) • Quasi-Experimental Designs • Pretest-posttest designs • Developmental designs (Longitudinal or cross-sectional) PSYC512: Research Methods

10. Combining Between-Subjects and Within Subjects Designs • The Mixed Design • Also known as “split plot” • Groups of subjects each receive a unique level of the between Ss variable(s) and all levels of the within Ss variable(s) PSYC512: Research Methods

11. Mixed Three-factor Design: Adding Presentation Order as a Factor to Account for Differential Carryover Presentation order Variable (between) Group A (control then pointing) Group B (pointing then control) Found 3-way interaction that indicates differential carryover (asymmetrical transfer) PSYC512: Research Methods

12. Combining Between-Subjects and Within Subjects Designs • Example of a Mixed Design • Task order manipulated between Ss • Group A (control then pointing) • Group B (pointing then control) • 3-way interaction indicates differential carryover effect (asymmetrical transfer) PSYC512: Research Methods

13. Combining Experimental and Correlational Designs • Covariates in experimental designs • Measure your subjects on a covariate—a variable that you believe may be correlated with your dependent variable • If left unmeasured these covariates add error variance and might obscure significant effects • Measuring the covariate allows you to use correlational statistical techniques in your analysis (e.g., Analysis of Covariance or ANCOVA) to “subtract out” the error variance associated with the covariate, thereby increasing the statistical power of your experiment • Example: measuring IQ in a learning experiment PSYC512: Research Methods

14. Combining Experimental and Correlational Designs • Quasi-independent variable in experimental designs • “Quasi” means “kind of, but not really” • Similar to including a covariate, except • measurement of covariate is used to assign Ss to groups • Covariate is thus treated as an quasi-independent variable • Quasi-independent variables are referred to as “quasi” because they cannot be manipulated, they are essentially dependent variables (measures) that are treated as independent variables in the experimental design and analysis PSYC512: Research Methods

15. Quasi-experimental Designs • Quasi-experimental designs are those in which only quasi-independent variables are used • Time series vs. pretest-posttest designs • Time series: Measure behavior several times prior to and following a treatment (time series design) or change in your quasi-independent variable (interrupted time series design) • Pretest-posttest: Measure behavior once prior to and once following the change in your independent variable PSYC512: Research Methods

16. Quasi-experimental Designs • Equivalent time samples design • Time-series design especially useful for treatments with transient effects • Repeatedly measure behavior following multiple applications and withdrawals of the treatment • Non-equivalent control group designs – helps control for history confounds which should affect both groups equally PSYC512: Research Methods

17. Developmental Designs • Used to assess changes in behavior related to a person’s chronological age, which serves as a quasi-independent variable • Cross-sectional designs • Simultaneously test subjects assigned to two or more age groups • Generational effects can confound the age variable • Longitudinal designs • Repeatedly test a single group of subjects over time • Controls for generational effects—but, may still limit external validity • May be confounded by history, mortality, and/or multiple observation effects • Cohort-sequential design • Combines longitudinal and cross-sectional designs by measuring multiple age groups over time which allows evaluation of generational or historical confounds PSYC512: Research Methods

18. Next Time… • More on experimentation • Small-n designs PSYC512: Research Methods