Generalizability Theory

An important criterion on which psychological measures are judged is the degree to which their scores reflect persons’ true standing on an attribute of interest (e.g., cognitive ability, conscientiousness). Measurement theories recognize that scores on a measure reflect at least two components: a true component and an error component. Although theories differ in terms of the way they define these components and the types of error on which they focus, they all share a concern for measurement error. Generalizability (G) theory is a measurement theory that provides methods for estimating the contribution of multiple sources of error to scores and quantifying their combined effect with a single index—a generalizability (G) coefficient.