Diagnosing Psychological Disorders

Foundations in Classification

• 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

Issues with Classifying and Diagnosing Psychological Disorders

• 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

History of the DSM

• 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

The DSM-5

• 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

Unresolved Issues in DSM-5

• 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