Assessment, Diagnosis, and Clinical Decision-Making
This domain tests psychometric reasoning, differential diagnosis, and culturally responsive assessment.
Core rules
- Reliability concerns consistency; validity concerns whether a test measures the intended construct. Sensitivity detects true cases; specificity detects true non-cases. Predictive values depend on prevalence, so a good test can have a low positive predictive value in a low-prevalence setting.
- Use multiple sources: case history, standardized tests, language sampling, dynamic assessment, classroom or workplace observation, and client-reported outcomes.
- In bilingual and culturally diverse clients, check test norms, dialect, education, and acculturation. Use interpreters appropriately and avoid translating standardized tests ad hoc.
Worked example
A screening test has 90% sensitivity and 80% specificity; prevalence in the clinic is 10%. Of 1000 clients, 90 true cases and 180 false positives are expected. Positive predictive value is 90/270, or 33%. A positive screen therefore requires diagnostic assessment, not automatic diagnosis. This is why base rates and referral context matter.
Traps that cost marks
- Treating a standard score as a diagnosis without functional evidence.
- Ignoring prevalence when interpreting screening results.
- Using one test to diagnose a complex communication disorder.
- Translating a test informally and treating the score as valid.