Generalizability Theory

Dan J. Putka

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, such as cognitive ability and 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, the degree of relation between them, and the types of error on which they focus, they all share a concern for measurement error. Generalizability theory (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 coefficient (G-coefficient). At the root of G-theory is the idea that the variability in persons' scores because of error (i.e., error variance ) can be partitioned into components, each reflecting a different source ...

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