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Why three tiers
Probability is not enough — clinical risk weights matter.
A purely Bayesian DDx ranks the most likely. A clinician also needs to track what would be catastrophic to miss. The third tier is a non-negotiable safety net for low-probability / high-impact diagnoses.
- Most likely · Highest posterior probability given evidence
- Differential to consider · Reasonable competitors deserving rule-out
- Don't miss · Suicide · psychosis · bipolar · medical mimics