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Validity and Reliability
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Says something about the meaning of the information obtained through an instrument ... Helps researchers make decisions related to what they studied ... – PowerPoint PPT presentation
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Title: Validity and Reliability
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Validity and Reliability
- EAF 410
- July 9, 2001
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Validity
- Degree to which evidence supports inferences made
- Appropriate
- Meaningful
- Useful
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Appropriate Inference
- Relevant to the study
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Meaningful Inference
- Says something about the meaning of the
information obtained through an instrument
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Useful Inference
- Helps researchers make decisions related to what
they studied
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Do we get useful information about the
topic/variables?
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Validity depends on
- The amount and type of evidence supporting the
interpretations
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Types of Evidence
- Content-related
- Criterion-related
- Construct-related
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Content-related
- Appropriate?
- Comprehensive?
- Logical?
- Adequate?
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- Adequacy of the sampling
- representative of content?
- Format of the instrument
- language, directions, etc.
- Who judges the validity of the content?
- Interpretation
- judgement
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Criterion-related
- Relationship between scores from different
instruments - Strong relationship?
- Accurate?
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- Instrument results compared with independent
criterion - a second test or measurement
- Predictive validity
- time between measurements
- Concurrent validity
- instrument and criterion measurements at same time
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- Validity Coefficient
- r correlation coefficient
- degree of relationship between scores from
instrument and criterion - Between -1.00 and 1.00
- .00 no relationship
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Construct-related
- How well does the theoretical construct account
for or explain differences? - Is the construct sufficient?
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- Three steps
- variable measured clearly defined
- hypotheses (based on theory)
- hypotheses tested logically and empirically
- Collect variety of different types of evidence
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Reliability
- Consistency of the scores
- among individuals
- among items
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- Reliable -- valid or not valid
- Not reliable -- not valid
- Validity and reliability dependent on the context
in which the instrument is used.
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Measurement Error
- Same test, different scores
- Caused by variety of factors
- motivation
- anxiety
- environment
- etc.
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Reliability Coefficient
- Reliability estimates
- Relationship between scores at two different
times, or - Relationship between two parts of the same
instrument
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Test-Retest
- Same test, same group, two times
- Reliability coefficient indicates relationship
between the two scores
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Equivalent-Forms
- Two different, equivalent tests, same group
- Reliability coefficient calculated
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Internal-Consistency
- Single administration of the instrument
- Split-half procedure
- Kuder-Richardson approach
- Alpha coefficient
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Split-Half Procedure
- Score two halves of test separately
- Degree to which the two halves provide same
results - Reliability increases with length of the
test/instrument
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Standard Error of Measurement
- Index showing how much a measurement would vary
under changed circumstances
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