Optimism bias: the tendency to overestimate the probability of positive events and underestimate that of negative ones


Optimism bias refers to the tendency for people to overestimate the probability of positive events while underestimating the probability of negative ones (Weinstein, 1984). In other words, people tend to perceive that they are less likely than other people to experience negative events. Optimism that is unrealistic corresponds to the underestimated risk in a range of situations such as job risk (Cooper, 2003), the risk of car accidents (DeJoy, 1989), and the risk from air pollution (Hatfield & Job, 2000). What is important to note here is that the optimism bias is greater for risks that are perceived as beneficial for individuals (for example, mobile phone radiation) than for those that affect society or the environment (e.g. GM food or climate change) (Costa-Font, Mossialos, & Rudisill, 2009). Also, optimism bias is larger for risks that infrequently occur than for those that are perceived as being more common (Harris, Griffin, & Murray, 2008).

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