Assessment, Diagnosis, and Psychological/Psychoeducational Testing
What to master
Assessment in child and adolescent psychology is multi-method, multi-informant, and multi-setting because children rarely refer themselves and behavior varies by context. Know psychometric foundations-reliability, validity, sensitivity, specificity, positive and negative predictive value-and how base rates change interpretation. Understand standard scores, percentiles, confidence intervals, standard error of measurement, and practice effects. Distinguish norm-referenced from criterion-referenced measures and curriculum-based measurement. Know DSM-5-TR differential diagnosis, comorbidity, and the difference between a clinical diagnosis and special education eligibility under IDEA or a Section 504 plan. Cultural and linguistic fairness, test adaptation, and use of interpreters are essential.
Traps
Common errors: interpreting subtest scatter as a profile without evidence; calling a percentile 'percent correct'; ignoring that confidence intervals overlap; relying on one informant; overpathologizing bilingual learners; and assuming a diagnosis automatically yields school services. Another trap is ignoring incremental validity-does the new test add information beyond what you already know?
Worked example / rule of thumb
A screener has 90% sensitivity and 90% specificity. In a 5% base-rate sample, PPV = (.90 × .05) / [(.90 × .05) + (.10 × .95)] ≈ 32%. Most positives are false positives. Rule of thumb: always ask what the prior probability is before interpreting a score.