STABILITY OF INDIVIDUAL-DIFFERENCES IN MULTIWAVE PANEL STUDIES - COMPARISON OF SIMPLEX MODELS AND ONE-FACTOR MODELS

The purpose of this investigation is to evaluate structural equation m odels (SEMs) for measures of the same construct collected on multiple occasions (one-variable, multiwave panel studies). Simplex models hypo thesize that a measure at any one wave is substantially influenced by the measure at the immediately preceding wave; correlations between th e same construct measured on different occasions are predicted to decl ine systematically as the number of intervening occasions increases. A lternatively, a one-factor model posits that a person's score at any o ne time is a function of some underlying ''true'' score and a random d isturbance that is idiosyncratic to the time; no temporal ordering of correlations is assumed. Both the simplex and one-factor models can be fit when there is only a single indicator of each construct at each wa ve (e.g., scale scores), but there are serious limitations to such mod els. Stronger models are possible when the same set of multiple indica tors (e.g., the items that make up the scale) is measured at each wave . In Study 1, based on students' evaluations of teaching effectiveness collected over an 8-year period, one-factor models fit the data well, whereas simplex models did not. In Study 2, based on personality vari ables collected over a 4-year period during adolescence, one-factor mo dels again provided an excellent fit to the data, whereas the simplex model did marginally poorer. The results challenge an overreliance on simplex models and demonstrate that a one-factor model is a potentiall y useful alternative that should be considered in multiwave studies.