Base Rate Neglect

Biological Parallel

A deer hears rustling in bushes—is it wind (base rate: 99%) or a mountain lion (base rate: 0.1%)? The deer flees anyway because vivid threat signals override statistical likelihood. Base rate neglect is adaptive when false negatives are catastrophic: better to flee from wind 99 times than ignore the one mountain lion. This 'smoke detector principle' pervades threat detection systems: alarm calls trigger fleeing even when most alarms are false, because the cost asymmetry (wasted energy vs. death) makes ignoring base rates rational.