The Longitudinal Guttman Simplex: A New Methodology for Measurement of Dynamic Constructs in Longitudinal Panel Studies

Traditional psychometric procedures can be inade quate for the measurement of dynamic constructs in longitudinal panel studies. This paper introduces an al ternative based on the longitudinal Guttman simplex (LGS) model, a measurement model developed espe cially for dynamic constructs measured longitudinally. The LGS is a model of cumulative, unitary develop ment. It is cumulative in the sense that as persons ac quire new skills (or abilities, or opinions), earlier ob tained skills are retained; it is unitary in the sense that all persons progress through a sequence of skills in the same skill order. CL, a consistency index that gives the researcher a measure of the extent to which the LGS model axioms are obeyed in a given dataset, is introduced. By making use of this consistency index, the researcher can develop scales uniquely sensitive to cumulative, unitary development. LGSCLUS, an explor atory procedure to find longitudinal Guttman scales in empirical datasets, is described. An artificial data study is reported, the purpose of which was to test the performance of LGSCLUS under controlled conditions. The artificial data study showed that, in general, LGSCLUS recovers longitudinal Guttman scales with a high degree of accuracy. There remains a need for measurement procedures for dynamic constructs exhib iting types of development other than cumulative and unitary. Index terms: Dynamic constructs, Gutt man simplex, Longitudinal panel studies, Mathemati cal models, Measurement theory, Scaling, Three-set data.