title: Optimal behaviour can violate the principle of regularity.
abstract: Understanding decisions is a fundamental aim of behavioural ecology, psychology and economics. The regularity axiom of utility theory holds that a preference between options should be maintained when other options are made available. Empirical studies have shown that animals violate regularity but this has not been understood from a theoretical perspective, such decisions have therefore been labelled as irrational. Here, I use models of state-dependent behaviour to demonstrate that choices can violate regularity even when behavioural strategies are optimal. I also show that the range of conditions over which regularity should be violated can be larger when options do not always persist into the future. Consequently, utility theory--based on axioms, including transitivity, regularity and the independence of irrelevant alternatives--is undermined, because even alternatives that are never chosen by an animal (in its current state) can be relevant to a decision.
authors.affiliation: Modelling Animal Decisions Group, School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK. pete.trimmer@gmail.com
authors.forename: Pete C
authors.initials: PC
authors.lastname: Trimmer
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D002755:Choice Behavior; D003657:Decision Making; D005247:Feeding Behavior; D008954:Models, Biological; D011235:Predatory Behavior
keywords: independence of irrelevant alternatives; natural selection; optimal decision-making; rationality; regularity; transitivity