The Science of Psychology

1. The Science of Psychology

2. Last week… • Science is a structured method of gaining new knowledge about the world • Scientific psychology has some unique problems: • Experimentation • Manipulate? • Measure?

3. Experimental Control • Extraneous Variables • Nuisance variables • Make the effects of the IV more difficult to determine • Participant characteristics • Unintended influences of experimental situation

4. Experimental Control • Extraneous Variables • Confounding variables • Influence the difference between groups • The differences observed between groups could be attributed to the IV or the confound

5. Experimental Control • Extraneous Variables • Experimenters • Physiological differences • Rosenthal effects

6. Experimental Control • Extraneous Variables • Participants • Demand characteristics • Good participant effect • Response biases

7. Basic Control Techniques • Randomization • Individuals have an equal chance of being assigned to any group in the experiment • Allows us to assume groups are roughly equivalent before administering the IV

8. Basic Control Techniques • Elimination • Extraneous variables are completely removed from the experiment

9. Basic Control Techniques • Constancy • An extraneous variable is reduced to a single value experienced by all participants • Standard control technique • Hold environment, temperature, lighting constant

10. Basic Control Techniques • Balancing and Counterbalancing • Balancing • Achieves group equality by distributing extraneous variables to all groups • Counterbalancing • Controls order effects by presenting treatments in a different sequence • Order or sequence effects • Carryover effects • Differential carryover

11. Basic Control Techniques • Within-Subject Counterbalancing • Within-Group Counterbalancing • Each treatment must be presented to each participant an equal number of times • Each treatment must occur an equal number of times at each testing session • Each treatment must precede and follow each of the other treatments an equal number of times

12. Participant 1 Participant 2 Participant 3 Participant 4 Participant 5 Participant 6 P C P C P C C P C P C P The Cola Wars!

13. Participant 1 Participant 2 Participant 3 Participant 4 Participant 5 Participant 6 P C DP P DP C C P DP C DP P DP P C DP C P The Cola Wars!

14. Basic Control Techniques • Single- and Double-Blind Experiments • The experimenter (single-blind) or both the experimenter and participants (double-blind) are unaware of the participants’ condition

15. Basic Control Techniques • Altering response sets • Rewrite survey items so that some negative responses indicate agreement and some positive responses indicate disagreement • Check for socially desirable responses in your survey and/or potentially undesirable cues