Glossary
Pessimism Bias
What is Pessimism Bias?
Pessimism bias means expecting outcomes to be worse than the available evidence warrants, such as overestimating an adverse event’s probability or underestimating a favorable one. A negative forecast is not necessarily biased: it can be accurate. Demonstrating bias requires a suitable comparison, such as observed frequencies or a well-supported probability estimate.
Pessimism bias versus optimism bias
Optimism bias involves expectations more favorable than the evidence warrants. Pessimistic expectations, low optimism and hopelessness overlap but are not identical measures. Likewise, judging one’s prospects against other people is a different question from estimating one’s absolute risk.
Pessimism bias example
A student may expect to fail despite doing well on comparable practice tests. To call that expectation biased, we would need to know how well those tests predict the exam. Preparation alone does not establish the correct probability.
Mental health evidence
A review of 22 longitudinal adolescent studies found that negative future-related thinking predicted later depressive symptoms and that depressive symptoms also predicted later negative future-related thinking. This does not prove a single causal direction or establish that each person’s expectations were inaccurate. The finding is not a diagnosis.
Normalcy bias concerns expecting familiar conditions to continue when a disruptive event is possible.