Testing the Ecological Rationality of Base Rate Neglect

What simple learning rules can allow agents to cope with changing environments? We tested whether a rule that neglects base rates of events in the world — something that is usually considered irrational — could be as successful as Bayesian inference — the usual standard of rationality — in making cuebased predictions about events in time-varying environments. We focused on environments in which base rates change more frequently than cue accuracies, a condition that, we argue, is common in the real world. Five strategies (Bayesian, cue accuracy alone, adjusted cue accuracy, base rates alone, and a Least Mean Square learning rule) were compared across “lifetimes” of 10,000 predictions, in which base rates and cue accuracy independently changed every 10, 50, 100, 500, 1000, or 5000 events. The results confirmed that simple strategies that are typically deemed irrational (base rate neglect and its opposite, conservatism) can rival the typical standard of rationality, Bayesian combination of information, by producing ecologically rational decisions in appropriately varying environments.