Base Rate Neglect
Probability matters before symptoms are interpreted.
Shrink Definition
Base rate neglect is the tendency to focus on vivid or individual information while overlooking how common or uncommon something actually is. In medicine, diseases don't all begin with equal probability. Some conditions are common. Others are exceptionally rare. Ignoring those background probabilities increases diagnostic error.
Plain language
Sometimes unusual stories distract us from what's statistically most likely.
Shrink Insight
Rare conditions happen. Common conditions happen far more often.
Why it matters
Clinicians constantly balance two questions: "What could this be?" "What's this most likely to be?" Good diagnostic reasoning answers both. Ignoring either creates unnecessary error.
Common misunderstanding
Considering base rates doesn't mean rare diseases should be ignored. It means rare diagnoses require proportionally stronger evidence.
Shrink Perspective
Good clinicians know zebras exist. They simply remember horses are more common.
Shrink Reflection
Have dramatic stories ever caused you to overestimate how often something happens?
Shrink Takeaway
Probability should guide curiosity, not replace it.
Medical boundary
This concept is educational and shouldn't be used to self-diagnose. It doesn't replace care from a licensed clinician. Symptoms, medication, and treatment decisions should be discussed with a qualified professional, and emergency symptoms require emergency care.
Evidence summary
Base rate neglect is one of the most extensively studied cognitive biases in psychology, behavioral economics, and medical decision making. Research consistently demonstrates that considering prior probability improves diagnostic accuracy.