Diagnosing specific learning disorder in adults Part II: bias, base rates, and a path forward

The diagnosis of specific learning disorders (SLDs) in adults has increased substantially over the past two decades, particularly within selective postsecondary and professional training settings. Part II of this paper examines why adult SLD diagnosis is especially vulnerable to error and bias, despite diagnostic criteria requiring substantial, developmentally grounded academic impairment.

We synthesize empirical research from neuropsychology, education, and psychometrics to identify systematic sources of diagnostic distortion in adult SLD assessment. Particular emphasis is placed on statistical artifacts (e.g. restriction of range), base-rate neglect, contextual performance effects, performance validity, reliance on self-report, and the misapplication of sociostructural frameworks to clinical decision-making.

To combat overdiagnosis and ground diagnosis in empirically-supported practices, we propose a four-step diagnostic framework for first time diagnosis of SLD in adults: 1) Documented academic achievement below at least the 16^th percentile relative to the general population norms; 2) Clear evidence of onset in early school years, including impairment when scaffolding and supports are removed; 3) Evidence that academic difficulties persisted despite adequate educational opportunity and, when available, targeted intervention; and 4) Exclusion of contextual, motivational, neurological/medical, language, or instructional explanations.

Accurate diagnosis of SLD in adulthood requires population-referenced criteria, corroborated evidence of childhood onset, objective demonstration of current academic impairment, systematic exclusion of alternative explanations, and assessment of performance credibility. Adoption of a structured, evidence-based diagnostic framework is essential to preserving the scientific validity, ethical application, and equitable use of SLD diagnoses in adult educational and professional settings.