Psychometrics
The science of measuring psychological constructs—attitudes, abilities, personality traits—through standardized instruments. The discipline behind every validated questionnaire in UX research.
Definition: The science of measuring psychological constructs—attitudes, abilities, personality traits—through standardized instruments. The discipline behind every validated questionnaire in UX research.
Psychometrics is the science of measurement in psychology. It provides the theory and methods behind standardized instruments like the SUS, NPS, and personality inventories. When you administer a questionnaire and trust the score, that trust rests on psychometric foundations.
Core Concepts
- Construct validity: Does the instrument actually measure what it claims to measure? A "usability" questionnaire that mostly captures aesthetics has poor construct validity
- Internal consistency: Do the items in the instrument agree with each other? If one question measures something entirely different from the rest, the overall score is unreliable
- Test-retest reliability: Does the instrument produce consistent results when the same person takes it twice under similar conditions?
- Norms and benchmarks: Psychometric instruments are calibrated against large populations. Without norms, a raw score is meaningless—you need context to interpret it
Why It Matters for UX
Every time you use a standardized scale—SUS, NPS, NASA-TLX, AttrakDiff—you are relying on psychometric work. The scoring formulas, the interpretation thresholds, and the benchmarks all come from psychometric validation studies.
The Danger of DIY Questionnaires
Teams routinely create ad hoc surveys with unvalidated questions. These instruments have unknown reliability and validity. Your five-point "ease of use" question might correlate with nothing useful. Psychometrics is the discipline that separates measurement from guessing.
When a validated instrument exists for what you want to measure, use it.
Related Terms
System Usability Scale (SUS)
A 10-item standardized questionnaire that produces a score from 0-100 measuring perceived usability. The industry's most widely used instrument for benchmarking usability.
Reliability
The consistency of a research method—whether it produces similar results when repeated under the same conditions. About precision, not accuracy. A method can be reliable without being valid.
Validity
Whether a research method measures what it claims to measure. About accuracy, not precision. A method can be reliable (consistent) but not valid (accurate) if it consistently measures the wrong thing.