Reliability

The consistency of an assessment's results across repeated administrations and across items.

Reliability is the consistency of a test's results. A reliable assessment produces similar scores across repeated administrations under similar conditions, and across the questions within it.

Reliability is necessary but not sufficient for validity — a test can be highly consistent and still measure the wrong thing. Common types include internal consistency (do items on the same scale agree?), test-retest reliability (does the same person score similarly on two separate days?), and inter-rater reliability (do different raters score behaviors the same way?).

Validity — The extent to which a psychological assessment measures what it claims to measure.
Cronbach's alpha (α) — A statistical measure of how internally consistent the items on a scale are; ≥ 0.7 is typically acceptable.
Internal consistency — The degree to which items on a scale correlate with one another, suggesting they measure the same construct.
Test-retest reliability — The consistency of an assessment's results when the same person takes it twice, separated by time.

Reliability

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