Clinical validity and interpretation of the Gordon Diagnostic System in ADHD assessments.

Gordon Diagnostic System (GDS) data were analyzed for 165 referred children with ADHD combined type and 46 referred children without ADHD, 6-16 years of age. Results showed significant differences between children with and without ADHD on the GDS standard scores and the IQ-GDS differences scores. Using a GDS composite standard score of 13 points or more below IQ to classify children as having ADHD resulted in the highest diagnostic accuracy (86%), with positive predictive power equal to 91%, and negative predictive power 67%. Results for the GDS compared favorably with those reported for other continuous performance tests. The findings lend support to the GDS as a clinically useful component of an ADHD evaluation.