Diagnosing Psychological Disorders

Diagnostic classification * Assignment to categories based on shared attributes or relations * Classification is central to all sciences
Idiographic strategy: what is unique about an individual’s personality, cultural background, or circumstances
Nomothetic strategy: often used when identifying a specific psychological disorder, to make a diagnosis
Terminology of classification systems * Taxonomy: classification in a scientific context * Nosology: taxonomy in psychological/medical phenomena * Nomenclature: labels in a nosological

Categorical and dimensional approaches * Classical (or pure) categorical approach: strict categories * Dimensional approach: classification along dimensions * Prototypical approach: combines classical and dimensional views
Widely used classification systems * Diagnostic and Statistical Manual of Mental Disorders (DSM) * Updated every 10-20 years * ICD-10 * International Classification of Diseases * Published by the World Health Organization

Prior to 1980, diagnoses were made based on biological or psychoanalytic theory
Introduction of DSM-III in 1980 revolutionized classification * Classification now relied on specific lists of symptoms, improving reliability and validity * Diagnoses classified along five “Axes” describing types of problems
DSM-IV introduced in 1994 * Eliminated previous distinction between psychological vs organic mental disorders * Reflected appreciation that all disorders are influenced by both psychological and biological factors
DSM-IV-TR (“text revision” of DSM-IV) incorporated new research and slightly altered criteria accordingly

Basic characteristics * Removed axial system * Clear inclusion and exclusion criteria for disorders * Disorders are categorized under broad headings * Empirically-grounded, prototypic approach to classification
Adding new diagnoses: new disorder labels are created when groups of individuals are identified whose symptoms are not adequately explained by existing labels

The problem of comorbidity * Comorbidity: 2 or more disorders for the same person * High comorbidity is extremely common * Emphasizes reliability, maybe at the expense of validity
Dimensional classification * DSM was intended to move toward a more dimensional approach, but critics say it doesn’t improve much from DSM-V
Labeling issues and stigmatization * Some labels have negative connotations and may make patients less likely to seek treatment