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VOL. 2, ISSUE 1 (2026)
Intellectual and developmental disabilities: Definitions, diagnostic limitations, and cross-system classification
Authors
Harjit Singh, Kok Hwee Chia
Abstract
Intellectual and Developmental Disabilities (IDDs) represents a broad,
cross-disciplinary construct applied in literature across healthcare,
education, and social policy to describe lifelong neurodevelopmental conditions, which emerge during the
developmental period. However, the absence of IDD as a formal diagnostic
category within major nosological systems has contributed to conceptual
ambiguity, inconsistent assessment practices, and challenges in
interdisciplinary communication. The authors of this paper critically examine
the conceptual foundations of IDD, distinguishing the umbrella term from the
core diagnosis of intellectual disability (ID) and related
developmental conditions such as Global Developmental Delay (GDD) and specific
developmental disorders (SDDs). Drawing on contemporary diagnostic frameworks,
the authors evaluate the
limitations of the Diagnostic Statistical Manual-5th Edition-Text Revision (DSM-5-TR) in identifying
psychiatric comorbidities in individuals with IDDs and highlights the role of
the Diagnostic Manual-Intellectual Disability-2nd Edition (DM-ID-2),
as a necessary diagnostic companion. The Cognition-Conation-Affect-Sensation (CCAS) model is introduced
as an integrative lens for understanding the multidimensional functioning of
individuals with IDDs beyond deficit-based
interpretations. A comparative analysis of DSM-5-TR and the International Classification of Diseases-11th Revision (ICD-11) classifications
further clarifies areas of alignment and divergence in the conceptualization of
ID, GDD, and
developmental delays (DDs). Overall, the authors argue that
conceptual clarity, developmentally informed diagnostics, and systems-sensitive
frameworks are essential for accurate diagnosis, effective intervention
planning, and equitable support across clinical and educational settings.
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Pages:1-6
How to cite this article:
Harjit Singh, Kok Hwee Chia "Intellectual and developmental disabilities: Definitions, diagnostic limitations, and cross-system classification". World Journal of Research in Education, Vol 2, Issue 1, 2026, Pages 1-6
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