Measurement, Psychometrics, and Construct Validity
Measurement as the Foundation of Application
Why Measurement Matters
Applied psychology depends on measurement because interventions, diagnostics, and evaluations require observable indicators of latent constructs such as motivation, stress, competence, or prejudice.
Core Psychometric Concepts
Validation as an Ongoing Process
Validation is not a property of a test itself but of score interpretations in specific contexts. Evidence may include content representation, internal structure, relations to other variables, and response processes.
Classical Test Theory vs Item Response Theory
Classical Test Theory
- Focuses on observed score and error
- Simpler and widely used
- Less precise at item level
Item Response Theory
- Models item difficulty and discrimination
- Supports adaptive testing
- Strong for scale development and equating
Which statement is most accurate about validity?
Validity is about whether evidence supports a particular interpretation and use of scores.
Correct answer: Validity concerns evidence for score interpretation in a specific use
What does measurement invariance allow researchers to compare across groups?
Without invariance, group differences may reflect measurement artifacts rather than true differences.
Correct answer: Whether scores represent the same construct across groups or time.
Scale Development Pipeline
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Step 1: Define the construct and its theoretical boundaries.
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Step 2: Generate items from theory, interviews, and expert review.
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Step 3: Pilot test and inspect item functioning.
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Step 4: Evaluate factor structure and reliability.
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Step 5: Test validity evidence and invariance across relevant groups.
A measure that gives similar scores repeatedly is primarily demonstrating:
Reliability is consistency in measurement.
Correct answer: Reliability