Reliability

Reliability

The consistency of measurement in a test, indicating that the test scores do not vary significantly across different occasions or situations.

True score

The average score a person would obtain if they took a test an infinite number of times, representing the person's actual ability or characteristic being measured.

Variance of the observed score

The variability in the scores obtained by individuals on a test, which is influenced by both the true score and the measurement error.

Test-retest coefficient

A measure of reliability that determines the consistency of a test over time by correlating scores obtained on two separate administrations of the test.

Parallel forms coefficient

A reliability test that involves administering two different versions of a test to the same group of individuals to assess consistency in measurement.

Internal consistency coefficients

Methods used to estimate reliability by assessing the consistency of responses within a single test, including the split-half method, Kuder-Richardson method, and coefficient Alpha.

Split Half Method

A single test is seen as composed of two parts (parallel forms) measuring the same thing. Therefore, a test can be administered and separate scores assigned on two arbitrarily selected halves of the test.

What is used to measure reliability with Split Half Method?

Spearman-Brown Formula

Kuder-Richardson Method

Is a dichotomous test can be divided into many different ways, which may result in different scores for r. The idea behind this method is to take the average of the reliability coefficients from all the possible half splits as the overall reliability estimate. H

Coefficient Alpha

Since the Kuder-Richardson formulas are applicable only when the test items are scored 0 or 1. However the coefficient alpha is a general formula for estimating reliability when a test consists of items on which different scoring weights may be assigned to different responses.

Interscorer/interrater reliability

The degree of agreement or correlation between two or more scorers or raters when scoring or rating test responses.

Interpreting reliability coefficients

The threshold for a reliable test depends on its intended use, with a coefficient of at least .60 or .70 needed for group comparisons and a coefficient of at least .85 needed for individual score comparisons.

Variability and test length

Reliability coefficients tend to be higher when there is greater variability in test scores, item scores, and ratings.

Reliability of criterion-referenced tests

The reliability of tests designed to determine mastery of a specific skill is assessed using the coefficient of agreement and Cohen's Kappa Coefficient.

Generalisability theory

A perspective that considers the various sources of measurement error and their impact on reliability coefficients, emphasizing the importance of test administration conditions and the intended purpose of the test.