Type II errors in comparisons of dextral and sinistral groups.

Anomalous cerebral dominance can have multiple manifestations, e.g., left-eye preference or left-foot preference in the absence of left handedness per se. The 1987 estimate of prevalence of anomalous dominance in the population by Geschwind and Behan approaches 30%, three times the estimate obtained by using handedness alone as the sorting criterion. Accordingly, substantial numbers of subjects assigned to "dextral" groups may actually display other legitimate indicators of anomalous dominance. As such there is a tendency to commit Type II errors in studies in which handedness alone is used to represent the variance attributed to cerebral dominance. Accordingly, null hypotheses assessing the relations of cerebral dominance with dependent variables are accepted even though they may, in fact, be false.