began. Third, an early age of onset is relatively closely linked to conduct problems and similar externalizing behaviors, but there is little evidence that LR and externalizing symptoms are closely related (Schuckit and Smith, 2006; Schuckit et al., 2000). These data, however, do not definitively address the relationship of LR to age of onset, and this question deserves further exploration. Another issue related to LR is the question of whether the performance of the score is a function of the number of SRE items endorsed. Prior work has demonstrated little or no change in LR when analyses covary for the number of items endorsed or if values are converted to z scores adjusted relative to only those subjects who endorsed the same number of items (Schuckit et al., 2005, 2006, 2008c).
