A Vernacular for Linear Latent Growth Models

In its most basic form, latent growth modeling (latent curve analysis) allows an assessment of individuals’change in a measured variable X over time. For simple linear models, as with other growth models, parameter estimates associated with the α construct (amount of X at a chosen temporal reference point) and β construct (growth in X per unit time) are not invariant with respect to choice of reference point and time unit. Latent means, variances, and covariances change with different temporal metrics. This article offers a nomenclature for describing linear latent growth models, demonstrates how latent moment parameter estimates vary as a function of changes in the α reference point and in the β growth metric, and presents a set of useful scale-free statistics for describing the results of linear latent growth modeling. Three examples are presented, two with a measured outcome and one with a latent outcome, and implications for applied and methodological researchers are presented.