What Longitudinal Model Should I Choose?

With the growing availability of longitudinal data comes the question of what model to use? In an ideal world, theory and substantive arguments would be sufficiently clear to dictate one. But in practice, there is little guidance and academic fads or the practice in researchers' fields typically affect model choice. We illustrate how a general longitudinal model (LV-ALT) can help researchers in their selection. The LV-ALT model can specialize to other popular models such as the classic random or fixed effects, growth curve models, autoregressive, latent difference scores, and a variety of other hybrid structures. The LV-ALT model can help to defend the choice of one of these traditional models or it can suggest new hybrid models to consider. We illustrate our results with NLYS79 and Add Health data on self-reported health and an analysis from a paper recently published in Demography.