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# Measurement: Reliability and Validity - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about 'Measurement: Reliability and Validity' - billy

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Presentation Transcript
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

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

• Construct of interest

• corresponds to the IV

• “effect”

• Constructs of disinterest

• “systematic error”

• Non-systematic variation

• “random error”

• “error variance”

True Score

Random Error

Observed Score =

More Reliable:

Less Reliable:

Test 1

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Test 2

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Test 1

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Test 2

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Types of reliability

• Test-retest

• Internal Consistency

• Split-half

• Cronbach’s alpha: average of all possible split-half reliabilities

• Number of items

• High variation among individuals being tested

• Clear instructions

• Optimal testing situation

Types of Validity

• Face

• Content

• Criterion

• Concurrent

• Predictive

• Construct

• Convergent

• Discriminant

Score = effect + systematic + random error

• Systematic error:

threat to validity

• Random error:

threat to reliability