Another strategy to improve the ability to detect variants contributing to DSM-IV AD is to consider the severity of the AD. One approach is to analyze a quantitative variable representing the total number of criteria that a person endorses. Although multiple combinations of criteria and study characteristics may result in a similar criterion count 17, especially when fewer criteria are endorsed 18, this proxy for AD severity has been successfully employed in previous studies 19,20 as it makes no assumptions about the cut-off of three or more criteria as an index of “affection status” nor does it equate individuals with 1-2 criteria with those who endorse no criteria during their lifetime.
