Standard error of measurement (SEM)

An estimate of how much a person's observed score is expected to vary from their true score due to measurement error.

The standard error of measurement (SEM) estimates how much a person's observed score on an assessment is expected to vary from their "true" score due to random measurement error. It's expressed in the same units as the score itself.

SEM is used to build confidence intervals around individual scores — "Your score was 28, but the 95% confidence interval is 25 to 31." That honesty about uncertainty is especially important when a single point estimate sits near a cutoff. SEM depends on both the test's reliability and the standard deviation of scores in the population: more reliable tests have smaller SEMs.

Reliability — The consistency of an assessment's results across repeated administrations and across items.
Cronbach's alpha (α) — A statistical measure of how internally consistent the items on a scale are; ≥ 0.7 is typically acceptable.
Cutoff score — A specific value on an assessment used to classify respondents into categories. Not a diagnosis.

Standard error of measurement (SEM)

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