Experimental Design 3: Demand Characteristics

1. Experimental Design 3:Demand Characteristics Martin Ch. 4

2. Demand Characteristics • Definition: • Clues given to the participant about the point of the experiment • Examples: • Experiment title: The effects of horror movies on mood • Obvious manipulation: Ten psychology students looking straight up • Biased or leading questions: Don’t you think it’s bad to murder unborn children?

3. Reactions to Demand Characteristics • Cooperative • “You seem like a nice person: I’ll help you get the right results” • Defensive • “I don’t want to look stupid/evil. I’ll do what a smart/good person is expected to do (rather than what I normally would do).” • Noncooperative • “This experiment is annoying. Let me screw up the results.”

4. Sources of Demand Characteristic Effects • Societal values • Be cooperative, look smart, … • Experimenter expectancies • Consciously or unconsciously suggesting what outcomes are desired • Negative feelings about being in the experiment • Maybe as a result of previous bad experiences

5. How to Test for the Effects of Demand Characteristics • Both positive + negative test questions • Include other tests of social compliance • See if these tests relate to performance • Post-experiment debriefing • Placebo control

6. Placebo • What makes a good placebo? • Keep all the details the same, especially things the subject is likely to develop expectations about • When does the placebo effect work? • Cognitively penetrable processes

7. How to Minimize Demand Characteristics • Automation • Blind and double-blind • Multiple experimenters • Naturalistic observation • Neutral test questions

8. Demand CharacteristicsExample: Mental scanning rates • Cognitive penetrability

9. Experiment validity examples • Course evaluation • Use course evaluation forms to see which version of a class is better • Evaluation of effective student behaviors • Use essay test scores and questionnaire to see which studying behaviors lead to better learning