Using developmental trajectories to understand developmental disorders.
OBJECTIVE
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.


METHODS
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.


CONCLUSIONS
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.
Thomas
Michael S C
MS
Developmental Neurocognition Laboratoy, School of Psychology, Birkbeck College, University of London, London, UK. m.thomas@bbk.ac.uk
Annaz
Dagmara
D
Ansari
Daniel
D
Scerif
Gaia
G
Jarrold
Chris
C
Karmiloff-Smith
Annette
A
D002648:Child; D002657:Child Development; D002675:Child, Preschool; D003072:Cognition Disorders / Q000175:diagnosis / Q000523:psychology; D003430:Cross-Sectional Studies; D002658:Developmental Disabilities / Q000175:diagnosis* / Q000523:psychology*; D004314:Down Syndrome / Q000523:psychology; D006801:Humans; D007806:Language Disorders / Q000175:diagnosis / Q000523:psychology; D008137:Longitudinal Studies; D008569:Memory Disorders / Q000523:psychology; D018980:Williams Syndrome / Q000523:psychology