PSYC512: Research Methods Lecture 11

1. PSYC512: Research MethodsLecture 11 Brian P. Dyre University of Idaho PSYC512: Research Methods

2. Lecture 11 Outline • Causation and Experimentation • Experimental research designs • Reactivity • Within vs. between subjects designs • Condition ordering • Subject assignment • More on research design • Using 2 or more groups • Multifactor research – using two or more independent variables • Experimentation vs. Quasi-experimentation PSYC512: Research Methods

3. Experimental Designs • Manipulate one or more independent variables and observe effect on dependent variable • Possible to achieve strong internal validity if extraneous variables are carefully controlledcausation can be inferred! • Extraneous variables (subject and environmental you aren’t interested in) add error variance • Differences in treatments might be due to error variance rather than your manipulations! PSYC512: Research Methods

4. Experimental Research: Reactivity • Reactivity and the Hawthorne effect • Demand characteristics: cues in experiment that allow a subject to determine the experimenter’s purpose, hypotheses, or expectations • Good subject role: S produces expected effect • Faithful-subject role (neutral) • Negativistic-subject role: S sabotages expected effect • Countering demand characteristics • unobtrusive measures or observations done in the “field” • Deception • Withholding information PSYC512: Research Methods

5. Experimental Designs • Goal: minimize the amount of error variance and ensure that it doesn’t correlate with your independent variables • How? • Reduce error variance • Increase effectiveness (variance) of your IV by choosing more extreme treatments • Randomize error variance across groups through random assignment of subjects • Use inferential statistics to estimate the effects of error variance PSYC512: Research Methods

6. Features of Experimental Designs • Subject Assignment: Within-Subjects (repeated measures) vs. Between Subjects • Number of Independent Variables: Single factor (IV) vs. multiple factors (IVs) • Number of Dependent Variables: Single DV vs. multiple DVs (multivariate) PSYC512: Research Methods

7. Features of Experimental Designs • Factors that determine optimal subject assignment • If at all possible use a within-subjects design • Most efficient-requires fewest subjects • Statistically powerful: each subject acts as their own control – eliminates error variance due to subject variables • PROBLEM: Carry-over and ordering effects • If significant carry-over and ordering effects are expected then use a between-subjects design • Randomized Groups: if subject variables are not expected to covary with the measure • Matched Groups: if subject variables are expected to covary with the measure (some argue randomization is still better) PSYC512: Research Methods

8. Controlling for Carry-over and Order Effects • Balance carry-over and order effects across treatments • Randomization and Blocked Randomization • Counterbalancing of N treatments • Complete: present each subject with a unique order and use every possible order: requires N! orders/Ss • Partial (Latin Square): present each subject a unique order carefully chosen from a subset of all possible orders PSYC512: Research Methods

9. Constructing a Latin Square for N treatments • Randomly assign each treatment a number • Five treatments (A, B, C, D, E) are assigned (1, 2, 3, 4, 5) • Determine First Order using: 1, 2, N, 3, N-1, 4, N -2… A, B, E, C, D PSYC512: Research Methods

10. Constructing a Latin Square for N treatments • Fill in N-1 more orders by incrementing down and “wrapping”. For odd N, also use reverse orders N = 4 (4 Ss) N = 5 (10 Ss) A B D C A B E C D D C E B A B C A D B C A D E E D A C B C D B A C D B E A A E B D C D A C B D E C A B B A C E D E A D B C C B D A E PSYC512: Research Methods

11. Controlling for Carry-over and Order Effects • Minimize carry-over and order effects across treatments • Practice Sessions • Breaks • Make the treatment order a between-subjects independent variable • Creates a mixed design PSYC512: Research Methods

12. Controlling for Subject Variance in Between-subjects Designs • Random Assignment • Ensures subject characteristics don’t correlate with treatments, if you have enough subjects • Matched Groups • Assess participants on one or more characteristics that might correlate with the DV • Distribute like-participants to groups • Subject attrition could be a problem • Both methods attempt to equate the groups and treat subject variance as error variance PSYC512: Research Methods

13. Choosing the Number and Type of Independent Variables • Single factor (IV) vs. multiple factors (IVs) • Single factor designs are simpler but more limited in scope • Multiple factors allow for examining the synergistic effects of variables (interactions) • Parametric vs. Non-parametric Designs • Parametric: IV is quantitative (ratio or interval scale) • Non-parametric: IV is qualitative (nominal or ordinal scale) PSYC512: Research Methods

14. Experimental vs. Quasi-Experimental Research Designs • Experimental Research: random assignment of subjects to conditions • Quasi-experimental: assignment of subjects to groups based on a “subject variable” or measured attribute • Treats a DV as an IV in the hope of establishing causality • May be necessary in the context of field studies • Examples: age, income, test-performance • Problems • Confounding variables may covary with subject variable • Regression to the mean PSYC512: Research Methods

15. Next Time… • Multi-factor experimentation PSYC512: Research Methods