Stability coefficients in longitudinal studies

Abstract

Longitudinal studies of personality traits and intelligence have used an exponential function to relate the magnitudes of the correlations between occasions to the time interval. This exponential function is shown to be equivalent to a quasi-simplex model of a stationary process with constant reliability. Two numerical illustrations are provided that compare the least-squares fit of the logarithm of the exponential function to an analysis of the covariance structure. Index terms: change scores, covariance structure analysis, exponential function, LISREL, simplex, stability index.