Public Release: 

Study casts doubt on claim that people are over-optimistic

King's College London

A new study by King's College London, UCL and Birkbeck, University of London, casts doubt over claims that people are inherently over-optimistic or 'optimistically biased' about the future.

For many decades scientists have believed that people have an 'irrational optimism bias' - a tendency to underestimate their chances of negative experiences, while overestimating their chances of positive events.

Optimism bias is thought to have contributed to past financial crises and the failure of individuals to look after themselves (e.g. eating healthily to avoid obesity) or their environment (e.g. fighting climate change). The UK government even considers optimism bias when planning large infrastructure projects and deciding which projects should be funded (HM Treasury Green Book).

Research has most recently claimed that people fail to learn from bad news when told the actual chance of experiencing a negative life event (such as cancer). Such a failure to learn from bad news would result in an optimistic outlook (The Optimism Bias; Sharot, 2012). However, this new study, published today in Cognitive Psychology, demonstrates major flaws in this research supporting the existence of this optimism bias. According to the authors, prior studies have generated data patterns that look like people are being over-optimistic, when no such bias exists.

The researchers first found that people's failure to learn from bad news was reversed when they were considering their chance of experiencing a positive event (e.g. living past 90 years old). For these events, people learnt less from good news (i.e. learning their chance of living past 90 years old is higher than they originally thought).

The researchers subsequently created computerised simulations designed to behave in a completely rational way when faced with the same psychological tests used in previous research (e.g. learning from good vs bad news about future events). By definition, these simulations are not optimistic and thus will not show bias. However, these computer simulations produced the same pattern of data that is usually interpreted as showing optimism bias, due to the fact that belief scores changed more in response to good than bad news.

The study therefore shows how apparent optimism for negative events (and pessimism for positive events) can arise as a result of purely statistical processes. According to the authors, this supposed optimism bias is an artefact of the tests used to assess it, in conjunction with the rarity of negative events.

In addition to their simulations and analytical work, the researchers conducted five studies in which they corrected for these methodological problems as far as possible. In these improved studies they observed no evidence whatsoever for people learning more from good than bad news (i.e. no evidence for optimism bias).

Punit Shah from the MRC Social, Genetic and Developmental Psychiatry (SGDP) Centre at King's College London, said: 'There is ample evidence for optimism bias in various real-world situations - England football fans for example - but these instances simply show that certain people might be optimistic in certain situations; not that they are generally optimistic.'

Dr Adam Harris from UCL said: 'Previous studies, which have used flawed methodologies to claim that people are optimistic across all situations and that this bias is 'normal', are now in serious doubt. We need to look for new ways of studying optimism bias to establish whether it is a universal feature of human cognition or not.

'This assumption that people are optimistically biased is being used to guide large infrastructure projects, with the aim of managing expectations around how much projects will cost and how long they will take to complete. Our research supports a reexamination of optimism bias before allowing it to guide clinical research and policy.'


The research was supported by the Experimental Psychology Society, the Medical Research Council and Wellcome [099775/Z/12/Z].

Notes to editors

For further media information please contact Jack Stonebridge, Press Officer, Institute of Psychiatry, Psychology & Neuroscience, King's College London or 07718697176.

About King's College London -

King's College London is one of the top 20 universities in the world (2015/16 QS World University Rankings) and among the oldest in England. King's has more than 26,500 students (of whom nearly 10,400 are graduate students) from some 150 countries worldwide, and nearly 6,900 staff. The university is in the second phase of a £1 billion redevelopment programme which is transforming its estate.

King's has an outstanding reputation for world-class teaching and cutting-edge research. In the 2014 Research Excellence Framework (REF) King's was ranked 6th nationally in the 'power' ranking, which takes into account both the quality and quantity of research activity, and 7th for quality according to Times Higher Education rankings. Eighty-four per cent of research at King's was deemed 'world-leading' or 'internationally excellent' (3* and 4*). The university is in the top seven UK universities for research earnings and has an overall annual income of more than £600 million.

King's has a particularly distinguished reputation in the humanities, law, the sciences (including a wide range of health areas such as psychiatry, medicine, nursing and dentistry) and social sciences including international affairs. It has played a major role in many of the advances that have shaped modern life, such as the discovery of the structure of DNA and research that led to the development of radio, television, mobile phones and radar.

King's College London and Guy's and St Thomas', King's College Hospital and South London and Maudsley NHS Foundation Trusts are part of King's Health Partners. King's Health Partners Academic Health Sciences Centre (AHSC) is a pioneering global collaboration between one of the world's leading research-led universities and three of London's most successful NHS Foundation Trusts, including leading teaching hospitals and comprehensive mental health services. For more information, visit:

About Wellcome -

Wellcome exists to improve health for everyone by helping great ideas to thrive. We're a global charitable foundation, both politically and financially independent. We support scientists and researchers, take on big problems, fuel imaginations and spark debate.

About Cognitive Psychology

Cognitive Psychology is concerned with advances in the study of attention, memory, language processing, perception, problem solving, and thinking. Cognitive Psychology specializes in extensive articles that have a major impact on cognitive theory and provide new theoretical advances. Research areas include: artificial intelligence, developmental psychology, linguistics, neurophysiology and social psychology.

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