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# Psychological testing: reliability, validity and norms

- Concept

A good test gives the same result when nothing has changed (reliable) and truly measures what it claims to measure (valid).

Updated Nov 5, 2026

## Key points

- Reliability = consistency; validity = accuracy (measures what it should).
- A test can be reliable but not valid; it cannot be valid without being reliable.
- Reliability types: test-retest (over time), inter-rater (between examiners) and internal consistency (items agree with each other).
- Validity types: content (covers the whole domain), construct (measures the theoretical concept) and criterion (agrees with an outcome, now or later).
- Standardization means identical administration and scoring; norms come from a large, representative sample.
- Standard scores: IQ-type scores have mean 100 and SD 15; T scores have mean 50 and SD 10.

## What it is

Psychological tests turn behavior, abilities or symptoms into scores. To be useful, a test must be standardized (given and scored the same way every time), reliable (consistent) and valid (accurate for its purpose), and its scores must be compared with norms from a representative reference group. Reliability is necessary but not enough: a test can be consistently wrong. These same ideas apply to rating scales, screening questionnaires and clinical examinations.

## Key facts

- Test-retest reliability is best reported as an intraclass correlation coefficient; inter-rater agreement often as kappa; internal consistency as Cronbach's alpha.
- Criterion validity is concurrent when compared with a reference standard at the same time, and predictive when compared with a later outcome.
- Face validity is whether a test looks, to the person taking it, as if it measures what it claims; it is the weakest form.
- Norms must match the person tested: a test normed in another country, language or generation can mislead.
- Scores drift upward over generations (the Flynn effect), so old norms overestimate performance.
- For screening tools, sensitivity and specificity describe validity against a diagnostic reference.

## Reliability and validity, with an example

| Property | Type | Question it answers | Example |
| --- | --- | --- | --- |
| Reliability | Test-retest | Same result when repeated? | A memory test gives similar scores two weeks apart in a stable patient |
| Reliability | Inter-rater | Do two examiners agree? | Two nurses score the same patient's agitation scale almost identically |
| Reliability | Internal consistency | Do the items measure the same thing? | All items of a sadness scale rise and fall together |
| Validity | Content | Does it cover the whole domain? | A depression scale asks about sleep, appetite and energy, not only mood |
| Validity | Construct | Does it measure the concept in theory? | An anxiety scale correlates with other anxiety measures, less with unrelated traits |
| Validity | Criterion (concurrent) | Does it agree with a reference now? | A screening questionnaire agrees with a structured diagnostic interview |
| Validity | Criterion (predictive) | Does it predict a later outcome? | An entrance exam score predicts first-year grades |

## Clinical notes

- A clock that always runs ten minutes fast is perfectly reliable and never valid: the same logic applies to a badly calibrated questionnaire.
- Test results are interpreted with education, language, culture, sensory limits and mood of the person in mind.

## Memory aid

Reliable repeats; valid is on target: a dart player who always hits the same wrong spot is reliable but not valid.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the difference between reliability and validity?

Reliability is consistency of results; validity is whether the test measures what it is meant to measure.

## Two psychologists score the same interview and agree closely. Which property is shown?

Inter-rater reliability.

## Can a test be valid without being reliable?

No. Reliability is necessary for validity, but a reliable test can still be invalid.

## A test score predicts later job performance. Which type of validity is this?

Predictive criterion validity.

## What are norms in psychological testing?

Reference scores from a large, representative group, used to judge how one person's score compares with others.

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## Connections

## Related 3

- [Intelligence testing and IQ](https://durgical.com/en/behavioral-science/intelligence-testing-and-iq/)
- [Personality tests: objective and projective](https://durgical.com/en/behavioral-science/personality-tests-objective-and-projective/)
- [Screening questionnaires in primary care](https://durgical.com/en/behavioral-science/screening-questionnaires-in-primary-care/)

[← All of behavioral science](https://durgical.com/en/behavioral-science/)

Educational content on behavior and the clinical relationship; not a diagnostic or treatment guide and no substitute for assessment by a health professional. If you or someone near you is at risk, seek help now from an emergency service or a mental-health helpline.

Sources: [A primer on reliability testing of a rating scale](https://pmc.ncbi.nlm.nih.gov/articles/PMC12331005/) (Indian Journal of Psychiatry (PubMed Central), 2025); [Psychometrics: Trust, but Verify](https://pmc.ncbi.nlm.nih.gov/articles/PMC10704389/) (Anesthesia & Analgesia (PubMed Central), 2019); [Assessment of Specific Learning Disabilities and Intellectual Disabilities](https://pmc.ncbi.nlm.nih.gov/articles/PMC10795803/) (Assessment (PubMed Central), 2023).

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Representative model, for educational purposes only.

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