Assessment, Diagnosis, and Clinical Decision-Making
Domain 5 tests psychometrics, test selection, differential diagnosis, and clinical reasoning. You must know reliability, validity, sensitivity, specificity, norm-referenced versus criterion-referenced assessment, dynamic assessment, and culturally and linguistically appropriate practice.
Core rules
- Reliability concerns consistency; validity concerns whether a test measures what it claims. Standard scores compare performance with a normative sample; criterion-referenced measures compare with a defined skill standard.
- Sensitivity is the probability of a positive finding when the condition is present; specificity is the probability of a negative finding when it is absent. Positive predictive value depends on prevalence, so a good test can still have many false positives in a low-prevalence setting.
- Use multiple sources: case history, standardized and nonstandardized measures, language sampling, observation, teacher/caregiver report, and response to intervention. Dynamic assessment helps separate difference from disorder.
Worked example
A screening test has 90% sensitivity and 80% specificity in a setting where 10% of children have the disorder. For 1,000 children, 90 true positives and 180 false positives are expected, so positive predictive value is 90/270, or 33%. That means a positive screen is a prompt for diagnostic assessment, not a diagnosis. The reasoning uses both test accuracy and base rate.
Traps
Do not apply norms from the wrong age, language, or population. Do not violate basal or ceiling rules. Do not equate eligibility with a full diagnosis. Do not rely on one score when functional evidence contradicts it. Do not ignore cultural and linguistic validity.