The Negative Contingency Illusion: A Cognitive Bias Leading to Misjudgement of Protection

Abstract Humans possess a highly adaptive ability to draw inferences about the world by recognizing meaningful links between stimuli and events: making contingency judgements. We describe a systematic bias in contingency judgements that we label the negative contingency illusion in which individuals falsely judge a cue to be protective against an outcome. We demonstrate that the illusion arises when outcome probability is low and occurs when there is no actual relationship between cue and outcome and even when there is a modest positive relationship between cue and outcome. Such misjudgements may lead individuals to superstitious beliefs and could have major public health implications if they lead to the belief in and promotion of treatments that are ineffective or deleterious to the prevention and treatment of illness.