01C-1-1 (2)

Approach independent variable dependent variable

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Unformatted text preview: of variables of • Issues of reliability and validity Issues reliability validity Determining Cause & Effect: Determining The Experimental Approach Independent Variable Dependent Variable •Random assignment + Control of extraneous variables = Internal Validity Internal •Representative sample + Psychological realism = External Validity External The Experimental Approach - An Example: Rosenthal & Jacobsen Example: Teacher Expectancy Change in IQ Score •“Bloomer” label assigned randomly + students /parents unaware of label = High Internal Validity Internal •Sample of varied ethnicity, ability etc. + Real classroom, real IQ tests = High External Validity External Did Rosenthal & Jacobsen Did prove SFP to be true? • • • • Could this outcome be due to chance Could variation and not the effect of the IV? What is the likelihood that this outcome is What due to chance? due If it’s < 5% (i.e., p < .05), we decide that the If result is statistically significant statistically What factors affect significance? • Magnitude of effect • Variability in data • Sample size We NEVER prove anything in We psychological research because We study samples, not populations We We draw inferences about populations We using data obtained from samples using Therefore, any result can be due to chance Therefore, alone alone It’s always a question of probability, never It’s of certainty of Statistical vs. Practical Significance Practical We have Statistical Significance whe...
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