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Chapter 9 – Lecture 8. Some ways to control threats. General control procedures Control over subject and experimenter effects Control through participant selection and assignment Control through specific experimental design. 1. General Control Procedures. Control over research setting. Lab
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Some ways to control threats • General control procedures • Control over subject and experimenter effects • Control through participant selection and assignment • Control through specific experimental design
1. General Control Procedures Control over research setting Lab ++internal validity --generalization Applied setting --internal validity ++generalization • Natural environment • In the lab • Stanford Prison Experiment - the psychological effects of becoming a prisoner or prison guard. - set up a simulated a prison
Planned simulation of 2 weeks (1971) N = 24 college students from the U.S. $15/day by participating in a study Flip of coin prisoner & guard basement of Stanford's Psychology Department building
Response Measurement • Focus on the DV: careful selection of the measurement • make sure measure is validated (scale)…reliable • (scale development) Replication Pilot experiment Exact replication
2. Control over Subject & Experimenter effect - motivation - knowledge - expectations blind & double blind procedures Experimenter knows the hypothesis, subject assignment etc… Blind: research assistant “blind” to assignment into a group Double Blind: both RA & Subject do not know (drug studies/ light therapy)
Automation: reduce experimenter/subject contact (tape recording etc) instructions computer testing • Objective measures (subjective DV) stereotyping/prejudice/in group/out group (RT) • Multiple observers & multiple experimenters: interrater reliability (Kappa) • Using deception: obscure the true hypothesis (vodka) deliberately misinform the participants (debrief!!) (confederate) (vodka study)
3. Control through subject selection & assignment • Random Sampling!!! Everyone has = chance & selections do not affect each other only way to control for unknown factors (potential confounds) Potential confounds are evenly distributed! • Subject Assignment – random assignment!!! free random assignment (use random number table) matched random assignment – (age, weight) 1 2 3 Unbiased sample Table of random # or r# generator General Population Everyone.. Target population Representative sample (n)
Control through subject selection & assignment Stratified random sampling: • Define exactly what target pop is based and match proportion in the population General Population Everyone.. Target population Representative sample (n)
4. Control over experimenter design Simple Pretest-posttest design Pretest-posttest, control group design