Validity Validity of measurement Validity of research
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Presentation on theme: "Validity Validity of measurement Validity of research"— Presentation transcript:
1 Validity Validity of measurement Validity of research Does it measure what it is supposed to?Validity of researchDoes it prove what it is supposed to?(Does it support the conclusion that it is supposed to?)
2 Validity of Research Internal Validity Construct Validity Does the IV (and not some other factor) really cause the changes in the DV?Ruling out other causes (confounds)Construct ValidityDoes the study support the theory it is supposed to and no other theories?Ruling out other theories (alternative explanations)External ValidityDo the results generalize to other people?Statistical ValidityDoes the IV cause the changes in the DV, or could they be due to chance?
3 The two kinds of Construct Validity Construct validity of measuresDoes it measure what it is supposed to and nothing else?Construct validity of researchDoes it support the theory it is supposed to and no other theories?
4 Threats to Validity Internal Validity: Confounds Construct Validity: AmbiguityExternal Validity: UniquenessStatistical Validity: Insufficient Power** and improper use of statistical techniques
5 Threats to Internal Validity: Confounds HistoryMaturationTesting effects (e.g.: practice effects)Selection bias (in assigning to conditions)MortalityRegression to the mean
6 Threats to Construct Validity: Ambiguity Loose connection between theory and method (poor operational definition of theoretical concepts)Ambiguous effects of IVsIf participants interpret the instructions differently than intended“Good subject” effectsEvaluation apprehension
7 Threats to External Validity: Uniqueness External validity = generalizabilityNon-representative samplesChanges over time“Ecological validity” – does the result transfer to the real world from the laboratory?The more unique the experimental situation and the sample, the less generalizable the results are likely to be
8 Threats to Statistical Validity: Insufficient Power Too small a sample size makes it harder to tell whether an effect is due to chance or notOther threats besides low power: There are many ways that the improper use of statistical techniques can lead to invalid conclusions.