Attention deficit hyperactivity disorder (ADHD), caffeine dependence (CaD) and sensation seeking (SS) were assessed only at the MM3 interview (n~1750). As outlined elsewhere (Edwards & Kendler, 2012), ADHD was assessed retrospectively by 11 items that reflected DSM-IV criteria reported up to age 18 with the scores broken down into four approximately equal categories. As described previously (Kendler et al. 2008), CD was assessed by 11 items from the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) interview using a four-point scale (Bucholz et al. 1994) operationalizing DSM-III-R criteria, excluding the highly deviant A criteria 9 (forcing someone into sexual activity) and 13 (physically cruel to people). We used a criteria count for CD divided into four roughly equal groups. Caffeine dependence was defined using symptoms of caffeine tolerance from the SCID and caffeine withdrawal as defined by DSM-IV (Kendler et al. 2007). SS was assessed by a shortened version of the Zuckerman scale, which, similar to the NS scale, attempts to assess an individual’s propensity to seek out novel and exciting experiences (Zuckerman, 1994). Three representative items were (i) I
