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probability · medical · decision-tree

Probability Tree for Diagnosing a Rare Disease

Tipo Diagrama de flujoNorma Sugiyama layered DAG + orthogonal routingMotor schematex-flowchartActualizado 4/6/2026
Probability Tree for Diagnosing a Rare Disease
Drawing preview
El escenario

A patient with non-specific symptoms is tested for a rare disease with prevalence 0.1%. A screening test has 95% sensitivity and specificity, and the tree calculates the likelihood of each possible outcome, revealing the high risk of false positives despite the high specificity.

Qué hay en este dibujo

Lee las decisiones que hay detrás.

01

Whether to test given low prior probability

02Interpretation of a positive result

low positive predictive value despite high specificity

03Interpretation of a negative result

high negative predictive value reassuring

Use this pattern to analyze diagnostic strategies and communicate the impact of prior probability on test interpretation. Also applies to any sequential probabilistic decision, such as credit scoring or quality control sampling.

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