Intelligence after early brain injury. I: Predicting IQ scores from medical variables

To study how psychometric intelligence is related to early brain damage, the medical histories and Wechsler IQ scores of 407 subjects were analysed by multiple regression techniques. The study separated those medical variables that predicted IQ from those that did not, estimated the relative importance of the predictor variables as modifying influences on intelligence, and established the overall predictive power of significant variable sets. Intelligence varied with some aspects of brain damage but not with others. There was no single predictor of intelligence; instead, there were sets of predictors that operated in contexts of varying width and definition, each set having a different level of predictive power. Intelligence itself was diverse, with different predictive sets for Full Scale, Verbal, and Performance IQ. An analysis of the pattern and magnitude of the nonpredictive and predictive medical variables, and of the predictor variables vis-à-vis each other, reveals some of the principles by which verbal and nonverbal intelligence are represented in the young damaged brain.