Chapter 8part2 notes

Chapter 8part2 notes - Threats to Internal Validity 4....

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Chapter 8 part 2
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Eliminating Confounds At the end of an experiment we want to be confident that any differences between the experimental conditions that we observe are due to the manipulation of the IV and not due to extraneous variables
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Internal Validity Internal Validity: the degree to which we draw accurate conclusions about the effect of the independent variable An experiment is internally valid when the researcher eliminates all potential sources of confound variance Achieved through strict experimental control Otherwise, confounding occurs
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Threats to Internal Validity 1. Biased Assignment to Conditions Differences in groups or conditions 2. Attrition Loss of participants (death, disinterest, embarrassment) Differential attrition 3. Pretest Sensitization Pretest affects results Example: cultural literacy becomes more relevant after pretest – affects learning rates
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Unformatted text preview: Threats to Internal Validity 4. History Previous levels of experience 5. Maturation Changes in age 6. Miscellaneous Design Confounds other systematic differences Internal Validity (contd) Experimenter Expectancy Effects Demand Characteristics Placebo Effects Sources of Error Variance Error variance = unsystematic, uncontrolled, unidentified error 1. Individual Differences 2. Transient States 3. Environmental Factors 4. Differential Treatment 5. Measurement Error The Problem of Generalizability When we exercise strict experimental control we sometimes create a highly specific or even artificial environment External Validity : the degree to which the results obtained in one study can be replicated or generalized to other samples, research settings, and procedures...
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This note was uploaded on 03/30/2008 for the course PSYC 2094 taught by Professor Trcunningham during the Fall '07 term at Virginia Tech.

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Chapter 8part2 notes - Threats to Internal Validity 4....

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