Lichten and Simon (2007) argued for the use of a Total Quotient (TQ) that combines existing IQ and adaptive functioning scores into a single index. They proposed that the TQ index will improve the accuracy of mental retardation diagnoses in court cases, particularly in capital cases, and, hence, would make a court's decisions fairer and more consistent. The TQ combines scores from standardized intelligence tests and adaptive behavior scales and is said to exhibit greater divergent validity than either separate measure, as indicated by the modest correlations between the sets of scores that represent the two domains. Simon and Lichten argued that the current diagnostic standard (i.e., a score of at least two SDs below the mean on both standardized intelligence and adaptive behavior measures) reduces the prevalence rate of mental retardation by a factor of at least 10, depending on the exact...

You do not currently have access to this content.