Optimism bias is typically measured through two determinants of risk: absolute risk, where individuals are asked to estimate their likelihood of experiencing a negative event compared to their actual chance of experiencing a negative event (comparison against self), and comparative risk, where individuals are asked to estimate the likelihood of experiencing a negative event (their personal risk estimate) compared to others of the same age and sex (a target risk estimate). Problems can occur when trying to measure absolute risk because it is extremely difficult to determine the actual risk statistic for a person. Therefore, the optimistic bias is primarily measured in comparative risk forms, where people compare themselves against others, through direct and indirect comparisons. Direct comparisons ask whether an individual's own risk of experiencing an event is less than, greater than, or equal to someone else's risk, while indirect comparisons ask individuals to provide separate estimates of their own risk of experiencing an event and others' risk of experiencing the same event.