Experiments and Observational Studies

1. Experiments and Observational Studies Ch. 13

2. Coaching Experiment • Factors • Yelling at players • Physical Abuse • Levels • Yelling: not at all/all the time • Physical Abuse: not at all/all the time

3. Coaching Experiment • Treatments • No yelling, no abuse • Yelling, no abuse • No yelling, abuse • Yelling, abuse

4. Coaching Experiment • Participants • 120 soccer players • Blocks • Freshmen Girls • Freshmen Boys • JV Girls • JV Boys • Varsity Girls • Varsity Boys

5. Diagraming the Experiment Random Treatment A Treatment B 20 Varsity girls Compare match performance Treatment C Block Treatment D 120 soccer players Random Treatment A Treatment B 20 Varsity boys Compare match performance Treatment C Treatment D

6. Control Group • Provides a baseline for comparing the effects of the other treatments

7. Placebo • Sometimes participants in a treatment group will show a change in the response variable just because they know they are in the treatment group • we try to make the treatment group and the control group as similar as possible by using a dummy treatment called a placebo • Placebo effect – participants in the control group show a change in the response variable

8. No Special Treatment for Treatments • People who may influence the results or people who evaluate the results may have bias for or against treatments • Try to eliminate the sources of bias by blinding • Single-blind – all influencers or all evaluators are blinded • Double-blind – all influencers and all evaluators are blinded

9. What Can Go Wrong • Lurking variable – a variable the is not among the explanatory variables in a study but that may influence the response variable • Confounding – when two variables are associated in such a way that their effects on a response variable cannot be distinguished