Judgment pitfalls in estimating premorbid intellectual function.

Neuropsychological diagnosis first requires estimation of patients' premorbid cognitive ability. Although a number of methods have been proposed for this purpose, in practice there is little standardization. Often, clinical judgment and expert synthesis of multiple sources of information are prescribed to derive a premorbid estimate. There are, however, a number of systematic biases in human cognition that may lead clinicians to produce inaccurate estimates of premorbid function. This paper reviews the cognitive biases that are most likely to interfere with clinical judgment in this context. Given findings in the human judgment literature, actuarial strategies are recommended to avoid the contamination of cognitive bias.