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# Measurement: Reliability and Validity

Measurement: Reliability and Validity. For a measure to be useful, it must be both reliable and valid Reliable = consistent in producing the same results every time the measure is used Valid = measuring what it is supposed to measure. Reliability.

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## Measurement: Reliability and Validity

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1. Measurement: Reliability and Validity • For a measure to be useful, it must be both reliable and valid • Reliable = consistent in producing the same results every time the measure is used • Valid = measuring what it is supposed to measure

2. Reliability Observed Score = true score + systematic error + random error • Observed Scores are the data gathered by the researcher • True Scores are the actual unknown values that correspond to the construct of interest • Systematic Error is variations that results from constructs of disinterest • Random Error is nonsystematic variations in the observed scores

3. Sources of Variability • Construct of interest • corresponds to the IV • “effect” • Constructs of disinterest • “systematic error” • Non-systematic variation • “random error” • “error variance”

4. Systematic Error True Score Random Error Observed Score = More Reliable: Less Reliable:

5. How many o’s? Test 1 Xxxxxoxxxxxxxxxxoxxxxxxxxxxxxxoxxxxxxxxxxoxxxxxxxaxxxxxxxxxxuxxxxoxxxqxxxxxxxc Test 2 Xxxxxoxxxxxxxxxxoxxxxxxxxxxxxxoxxxxxxxxxxoxxxxxxxaxxxxxxxxxxuxxxxoxxxqxxxxxxxc

6. How many o’s? Test 1 Xxxxxoxxxxxxxxxxoxxxxxxxxxxxxxoxxxxxxxxxxoxxxxxxxaxxxxxxxxxxuxxxxoxxxqxxxxxxxc Test 2 Xxxxxoxxxxxxxxxxoxxxxxxxxxxxxxoxxxxxxxxxxoxxxxxxxaxxxxxxxxxxuxxxxoxxxqxxxxxxxc

7. How do we determine whether a measure is reliable? Types of reliability • Test-retest • Internal Consistency • Split-half • Cronbach’s alpha: average of all possible split-half reliabilities

8. Factors that increase reliability • Number of items • High variation among individuals being tested • Clear instructions • Optimal testing situation

9. How do we determine whether our measures are valid? Types of Validity • Face • Content • Criterion • Concurrent • Predictive • Construct • Convergent • Discriminant

10. Threats to reliability and validity Score = effect + systematic + random error • Systematic error: threat to validity • Random error: threat to reliability

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