We evaluated the statistical power of single-indicator latent growth curve models (LGCMs) to detect correlated change between two variables (covariance of slopes) as a function of sample size, number of longitudinal measurement occasions, and reliability (measurement error variance). Power approximations following the method of Satorra and Saris…

Demonstrating good reliability for the difference score in measurement, the results of this study indicate that the difference score is often highly reliable when the correlation between true change and true initial status is nonnegative. In general, when individual differences in true change are appreciable, the difference score shows strong…

Two sources of inconsistency were separated by reanalyzing data from a major study on short-term consistency. Little evidence was found for generalizability or behavioral predictability. Results supported the assumption that measurement error from short-term fluctuations is not due to systematic individual differences in response consistency.…