optimism bias

Meaning: Optimism bias is a cognitive bias in judgment in which people expect their own future to go better than the evidence, or the average person's outcomes, would support. A smoker may rate their own risk of lung disease below that of other smokers, or a student may expect to finish a project faster than similar past projects went. It is often explained by selective attention to favorable information and by motivation to protect self-esteem and reduce anxiety.

On the MCAT: A passage describes people estimating their own chance of a negative event, such as a car accident or divorce, compared with the average person. If the group's mean self-estimate falls below the true base rate, the group shows optimism bias. Questions may ask you to predict the behavioral effect: underestimating personal risk can lead to less use of seat belts, sunscreen or health screening. Others ask you to tell it apart from related biases.

Common confusion: Optimism bias is not the self-serving bias. The self-serving bias explains past outcomes (crediting success to oneself, blaming failure on the situation), while optimism bias predicts future outcomes. It is also an error in estimates, not a trait of cheerful people: the average risk cannot be below average for everyone, so widespread below-average self-ratings signal systematic error.