14%) were significantly more likely to report depressed mood as a symptom of nicotine withdrawal than men (AUS: 21%, FIN: 10%) and fewer cigarettes per day at peak lifetime use. In the Australian sample, women were also more likely than men to report irritability (AUS Women: 55%, AUS Men: 50%) and problems with concentration (AUS Women: 39%, AUS Men: 34%), while in the Finnish sample women were more likely to report impairment related to nicotine withdrawal compared to men (FIN Women: 14%, FIN Men: 9%). No other important sex differences were found. For the NW affected sib-pairs that were included in the non-parametric linkage analyses, rates of restlessness, concentration problems, decreased heart rate and increased appetite no longer differed significantly across the samples, and the number of NW symptoms were more comparable (mean = 4.4 FIN, 4.7 AUS). Tetrachoric correlations between DSM-IV NW and DSM-IV nicotine dependence (which includes NW as a symptom) were r = 0.73 and r = 0.72, but correlations between DSM-IV NW and a definition of nicotine dependence using a cut-off of 4 or more on the Fagerström Test of Nicotine Dependence (FTND; Heatherton et al., 1991; Heatherton et al., 1989; Breslau and Johnson, 2000; Saccone
