Assessment and Diagnosis
What to know
Understand psychometric foundations: reliability (test-retest, interrater, internal consistency) and validity (content, construct, criterion-concurrent and predictive), standard error of measurement, and the meaning of standard scores (z, T, IQ, percentile). Know purposes of assessment (screening, diagnosis, treatment planning, progress monitoring) and the difference between nomothetic and idiographic approaches. Familiarize yourself with diagnostic reasoning: differential diagnosis, comorbidity, base rates, and cultural/linguistic considerations in test selection. Understand informed consent for assessment, test security, and limits of competence.
Traps
Questions often confuse reliability with validity-a test can be reliable but invalid. Watch for items that describe a high score on one measure and ask about interpretation; consider the measure's norms and the referral question. Be alert to base-rate neglect: a highly sensitive test in a low-prevalence population still yields many false positives.
Rule of thumb
Reliability is necessary but not sufficient for validity. When interpreting any score, ask: compared with what norm group, for what purpose, and with what margin of error (SEM)?