Reliability

Precision

The estimated reliability and consistency of test scores across a sample or time.

Trueness

The accuracy or closeness of a measured value to the true value.

Measurement error

Factors associated with the process of measuring a variable, excluding the variable itself.

Random error

Inconsistencies in other variables during measurement, causing fluctuations.

Systematic error

Consistent error in measuring a variable, often proportional to the true value.

Reliability

The measure of consistency in test results under the same conditions.

Psychological measures

Assessments of psychological differences that rely on accurate measurement.

Classical test theory

A measurement theory defining reliability based on true scores and errors.

Observed score

The sum of the true score and measurement error in a test result.

Random error

Variability in observed scores that is expected to cancel out over multiple tests.

Sources of random error

Candidate-related, procedural, environmental, and test-related factors.

Test-retest reliability

Correlation of results from the same group tested twice over time.

Alternate forms reliability

Consistency measured by comparing results from two different versions of a test.

Interrater reliability

Agreement between multiple scorers on a measure.

Internal consistency

The degree of relatedness among items on a test measuring the same attribute.

Split-half reliability

Correlation between scores on two halves of a test.

Cronbach's alpha

Average correlation between all possible pairs of items on a test.

Standard error of measurement (SEM)

Precision measure indicating the error inherent in an observed score.