N 170 146 194 168 245 133 150 205 189 162 208 163 158 155 137 158 129 164 171 141 150 189 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Girls Total problems Externalizing problems Internalizing problems Aggressive behaviour Delinquent behaviour Anxious/depressed Somatic complaints Withdrawn Attention problems Social problems Thought problems Boys Total problems Externalizing problems Internalizing problems Aggressive behaviour Delinquent behaviour Anxious/depressed Somatic complaints Withdrawn Attention problems Social problems Thought problems Total problems Externalising problems Internalising problems Aggressive behaviour Delinquent behaviour Anxious/depressed Somatic complaints Withdrawn Attention problems Social problems Thought problems behaviour [21]. In children with attention problems, self-medication may contribute to the development of nicotine dependence since tobacco is known to amelio- rate symptom severity, and enhance general attention [22-24]. Self-medication may also apply to thought pro- blems as shown in schizophrenic patients [25,26]. We, Table 3 Odds ratios and 95% confidence intervals for tertiles of CBCL-scores; adjusted for age, mother’s education, and sex Tertile of CBCL-score Low (reference) Intermediate 6 (4%) 6 (4%) 8 (4%) 8 (5%) 8 (3%) 4 (3%) 7 (5%) 8 (4%) 4 (2%) 10 (6%) 4 (2%) 9 (6%) 13 (8%) 11 (7%) 10 (7%) 9 (6%) 10 (8%) 9 (6%) 12 (7%) 10 (7%) 11 (7%) 11 (6%) 1.4 (0.7;2.9) 0.8 (0.4;1.7) 1.2 (0.6;2.4) 0.9 (0.5;1.9) 1.7 (0.8;3.3) 1.1 (0.6;2.1) 1.2 (0.6;2.2) 1.1 (0.6;2.1) 1.6 (0.8;3.1) 1.0 (0.4;2.3) 2.8 (1.4;5.5) High 1.9 (09;3.7) 1.3 (0.7;2.5) 1.2 (0.6;2.4) 1.3 (0.7;2.5) 2.2 (1.1;4.4) 1.2 (0.6;2.5) 1.4 (0.7;2.8) 1.7 (0.8;3.3) 1.8 (0.9;3.5) 1.4 (0.8;2.6) 1.7 (0.8;3.3) de Meer et al. BMC Public Health 2010, 10:615 http://www.biomedcentral.com/1471-2458/10/615 Table 2 Number of ever smokers by tertiles of the distribution for CBCL Low Ever smokers Tertile of CBCL score Intermediate Ever smokers High Ever smokers p-value trend N 159 190 154 179 106 211 178 120 186 128 126 156 167 164 182 198 177 185 182 170 177 113 5 (3%) 7 (4%) 10 (6%) 6 (3%) 5 (5%) 11 (5%) 7 (4%) 6 (5%) 10 (5%) 5 (4%) 10 (8%) 15 (10%) 11 (7%) 11 (7%) 13 (7%) 15 (8%) 14 (8%) 13 (7%) 13 (7%) 9 (5%) 10 (6%) 11 (10%) N 163 156 144 145 141 148 164 167 117 125 158 149 143 149 149 112 162 119 115 157 141 166 13 (8%) 11 (7%) 6 (4%) 10 (7%) 11 (8%) 9 (6%) 10 (6%) 10 (6%) 10 (8%) 7 (6%) 10 (6%) 9 (6%) 9 (6%) 11 (7%) 10 (7%) 9 (8%) 9 (6%) 11 (9%) 8 (7%) 14 (9%) 12 (8%) 11 (7%) Page 4 of 6 0.062 0.211 0.911 0.412 0.050 0.237 0.544 0.352 0.010 0.783 0.039 0.827 0.508 0.925 0.845 0.437 0.445 0.227 0.990 0.516 0.708 0.737 however, emphasize that ‘thought problems’ in this study is not synonymous with psychiatric pathology. CBCL items for thought problems address problems with reality testing and obsessive/compulsive behaviour, though without a relationship with DSM-diagnoses. Since we did not collect data on any action to relieve symptoms, explanations with respect to self-medication for our results should be considered speculative. Never- theless, our results are in agreement with previous stu- dies that showed an earlier initiation of smoking in subjects with attention deficit or thought problems including schizophrenia [12,27,28]. It might be that chil- dren with symptoms of attention deficit or thought Table 4 Odds ratios and 95% confidence intervals for tertiles of CBCL-scores in girls; adjusted for age and mother’s education Tertile of CBCL-score Low (reference) Intermediate Total problems Delinquent behaviour Attention problems Thought problems 1.0 1.0 1.0 1.0 0.9 (0.3;3.1) 1.6 (0.5;4.9) 3.1 (0.9;10.3) 4.5 (1.4;14.9) High 2.7 (1.0;7.5) 2.8 (1.1;7.3) 3.6 (1.1;11.8) 3.7 (1.1;12.1)