Researchers who study intermediate cognitive and behavioral phenotypes in ADHD strive to reliably predict parent and teacher ratings of child behavior from performance on laboratory measures of cognitive functioning, and then link these associations to genes and biology. Unfortunately, it has been suggested that the investigation of endophenotypes for ADHD has been disappointing (Stevenson, Asherson, Hay, Levy, Swanson, Thapar & Willcutt, 2005). Several factors contribute to this lack of progress including incompatibility among labs in the tools that are used to measure behavioral variability. Hopefully our use of digit span, a working memory task that has been researched for over 100 years (Richardson, 2007), will increase the likelihood that others can replicate the current findings.
