Determination of an individual's level of intellectual functioning is a fundamental component of the neuropsychological assessment. Once established, general level of intelligence serves as a point of reference from which to evaluate performance in other domains. Intelligence encompasses a broad range of capacities, many of which are not directly assessed in the traditional clinical setting. The estimate of general intellectual ability is based on both formal assessment methods and a survey of demographic factors and life accomplishments. Formal measures of general intellectual function typically assess a broad range of functions through multiple subtests (e.g., WAIS-III, WASI, WISC-III), and yield an "intelligence quotient'' as well as other derived index scores. Other test instruments obtain high correlations with IQ measures and have been used to estimate overall intellectual ability (e.g., Ravens Progressive Matrices, Shipley Institute of Living Scale). In cases of known or suspected impairment, premorbid ability can also be surmised from performance on measures presumed less sensitive to cerebral dysfunction (e.g., vocabulary). Single-word reading tests (e.g., AmNART) have been used to estimate baseline verbal intelligence in patients with early degenerative conditions. In addition, so-called "best performance methods'' can be used. This method assumes that the patient's highest level of performance can be used to set a reference point for optimal baseline ability (Table I).
Demographic variables, including level ofeducation and professional achievement, avocational interests and pursuits, and socioeconomic status, can also be used to gauge an individual's current or premorbid general intellectual ability. Relationships among these variables are complex, and particular care must be exercised in the evaluation of patients from diverse sociocultural backgrounds. It is important to consider real-world accomplishments in the unique context of the individual, with attention to environmental factors that influence opportunity and achievement.
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