Assessment and Diagnosis: Test Selection, Administration, Interpretation, and Differential Diagnosis
Core concepts to master
Competent assessment begins with a referral question and a hypothesis-driven battery. Know the psychometric foundations: reliability, standard error of measurement, base rates, sensitivity/specificity, and the difference between normative and ipsative comparison. Understand premorbid estimation (demographic regression, word-reading tests, best-performance methods) and the limits of each. Interpretation requires integrating base rates of low scores in healthy people - multiple low scores are common and not automatically pathologic.
Differential diagnosis hinges on pattern recognition across domains plus history, onset, and course. Distinguish delirium from dementia, depression from pseudodementia, and normal aging from mild cognitive impairment. Validity testing (performance validity and symptom validity) is mandatory in forensic and high-stakes contexts.
Traps
Overinterpreting a single low score; ignoring the false-positive rate of fixed cutoffs; treating a screening instrument as diagnostic; and failing to consider effort, culture, language, education, and sensory/motor confounds. Questions may ask you to choose the next step - often validity testing or history-gathering rather than more tests.
Rule of thumb
Use a two-stage logic: (1) Is the data valid and the comparison appropriate? (2) Does the pattern fit a known profile better than alternatives? A diagnosis requires convergent evidence, not one aberrant score.
Worked example: A litigant with severe memory complaints but intact performance on forced-choice recognition and inconsistent effort indices should prompt validity concerns before any memory diagnosis.