Psychopathology and Diagnostic Assessment: Reliability, Validity, and Measurement
This domain tests whether you can reason about how we know what we know. Understand the distinction between reliability (consistency) and validity (accuracy), and the subtypes: inter-rater, test-retest, and internal consistency for reliability; face, content, criterion, and construct validity. Know that structured interviews improve reliability more than validity, and that DSM and ICD are categorical systems imposed on dimensional phenomena, which is why subthreshold and mixed presentations are common.
Key concepts
- Screening versus diagnostic instruments: sensitivity and specificity trade-offs, positive predictive value depending on prevalence.
- The mental status examination as a structured dataset: appearance, behavior, speech, mood and affect, thought process and content, perception, cognition, insight, judgment.
- Cognitive screening (MMSE, MoCA) and when formal neuropsychological testing adds value.
- Cultural formulation and the danger of pathologizing culturally normative experiences.
Traps
- Confusing a highly sensitive screen with a diagnostic test; a positive screen in a low-prevalence setting often is a false positive.
- Assuming a reliable diagnosis is a valid one.
- Overlooking collateral information and records when the interview is ambiguous.
Rule of thumb
Compute positive predictive value mentally: when prevalence is low, even a specific test yields many false positives. In vignettes, ask whether the question is about ruling out (favor sensitivity) or confirming (favor specificity).