Inverse fallacy

Biological Parallel

When predators detect prey odor, the conditional probability P(odor|prey present) ≈ 90%, but predators often act as if P(prey present|odor) ≈ 90%—ignoring base rates and false positive sources (decoy scents, old trails, non-prey animals). Bloodhounds following scent trails exhibit 95% sensitivity but achieve low positive predictive value when base rates are low: in searches for escaped prisoners (1 in 10,000 people), most scent matches are innocent hikers. Humans make identical errors: positive medical test (95% sensitivity) interpreted as 95% disease probability ignoring 1% base rate yields 16% actual probability, eyewitness identification (80% accurate) treated as 80% guilt probability ignoring lineup composition. Bayes' theorem is evolutionarily unintuitive.