Base Rate Neglect

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

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.