Introduction

This chapter discusses the association of several first-order growth curves with data at the same time points. This type of model is known as a parallel process model (PPM) or parallel process latent growth curve model. Because a PPM is considered a primer of a second-order growth curve, this chapter demonstrates how a PPM can be extended to a second-order growth curve in an incremental manner. First, this chapter provides an introduction to parallel process models (PPMs), including the estimation and interpretation of a PPM and when a PPM is appropriate. Second, the chapter introduces different specifications of associations among first-order growth factors within a PPM. Third, the chapter demonstrates how a PPM can be extended to a second-order growth curve model known as a factor-of-curves model (FCM). A FCM uses first-order growth factors as the indicators of second-order growth factors reflecting underlying global factors (i.e., intercept and slope factors of a global domain, such as internalizing symptoms).