Using Developmental Trajectories to Understand Developmental Disorders

TLDR

The article provides a tutorial on using developmental trajectories to study language and cognitive impairments in developmental disorders and compares this approach with matching. The authors evaluate the strengths, limitations, and practical implications of trajectory versus matching methods, illustrating the contrast with developmental delay versus atypical development. They conclude that trajectory analysis offers a richer descriptive vocabulary for understanding mechanisms and recommend combining cross‑sectional designs with longitudinal follow‑up to study developmental disorders.

Abstract

Purpose In this article, the authors present a tutorial on the use of developmental trajectories for studying language and cognitive impairments in developmental disorders and compare this method with the use of matching. Method The authors assess the strengths, limitations, and practical implications of each method. The contrast between the methodologies is highlighted using the example of developmental delay and the criteria used to distinguish delay from atypical development. Results The authors argue for the utility of the trajectory approach, using illustrations from studies investigating language and cognitive impairments in individuals with Williams syndrome, Down syndrome, and autism spectrum disorder. Conclusion Two conclusions were reached: (a) An understanding of the underlying mechanism will be furthered by the richer descriptive vocabulary provided by the trajectories approach (e.g., in distinguishing different types of delay) and (b) an optimal design for studying developmental disorders is to combine initial cross-sectional designs with longitudinal follow-up.