de Meer et al. BMC Public Health 2010, 10:615 http://www.biomedcentral.com/1471-2458/10/615 Table 1 Socio-demographic characteristics of smoking and non-smoking children Gender, N = 960: Boy Girl Age, N = 960: 9-10 years 11-13 years Ethnic origin, N = 960 Dutch Non-Dutch Family composition, N = 946 2 parents 1 parent Siblings, N = 960 0 or 1 2 or more Mother’s education, N = 931 University or high vocational Intermediate vocational Low vocational or high school Father’s education, N = 891 University or high vocational Intermediate vocational Low vocational or high school All (N = 960) 468 (49%) 492 (51%) 341 (36%) 619 (64%) 700 (73%) 260 (27%) 849 (90%) 97 (10%) 554 (58%) 406 (42%) 198 (21%) 272 (29%) 461 (50%) 254 (26%) 242 (27%) 395 (44%) Ever smoking No (N = 903) 435 (48%) 468 (52%) 329 (36%) 574 (64%) 653 (72%) 250 (28%) 801 (90%) 90 (10%) 518 (57%) 385 (43%) 182 (21%) 251 (29%) 442 (50%) 239 (28%) 222 (27%) 378 (45%) Yes (N = 57) 33 (58%) 24 (42%) 12 (21%) 45 (79%) 47 (82%) 10 (18%) 48 (87%) 7 (13%) 36 (63%) 21 (37%) 16 (29%) 21 (37%) 19 (34%) 15 (29%) 20 (28%) 17 (33%) Page 3 of 6 P-value 0.173 0.022 0.123 0.494 0.411 0.026 0.289 Aiming at a more precise assessment of the relation- ships within the uppermost tertile of CBCL scores for attention problems and delinquent behaviour, logistic regression was repeated for split groups of the uppermost tertile (67th - 83rd and >83rd percentiles). To increase sta- tistical power, the lowest and intermediate tertiles were combined as the reference group. As shown in Figure 1, for attention problems and delinquent behaviour only the uppermost 16.7% values of CBCL-scores were asso- ciated with ever smoking (P < 0.050). Discussion In this study, we found that among pre-adolescent girls smoking initiation was associated with delinquency, attention problems, and thought problems. For delin- quency and attention problems, this was limited to CBCL-scores in the subclinical and clinical range. In con- trast, the association of smoking initiation with thought problems applied to mild problems as well. In boys smoking initiation was not associated with problem behaviour. Our results confirms a relationship of smoking with attention deficit [16,17], conduct problems [4,7,18,19], delinquency and thought problems [8]. To our knowledge this is the first study that took into account the distribu- tion of the data on child behaviour by analyzing in tertiles. Theoretically, this provides information on the role of pro- blem behaviour beyond clinical cut-off values. Interest- ingly, our final results show that an association with smoking conferred the uppermost 16.7% of CBCL scores, i.e. close to the subclinical cut-off value of the uppermost 15% CBCL scores [14,15]. Our results thus suggest that smoking prevention will benefit most from targeting a ‘high-risk’ group of chil- dren with behavioural problems. The association of smoking initiation with specific domains of problem behaviour may be taken into consideration as an addi- tional reason for a ‘high-risk’ group approach. This may be added to general population strategies for smoking prevention, thereby increasing its effect in the subgroup of children with behavioural problems. To our opinion, this is a relevant group for smoking prevention since early starters have been shown at high risk of regular use, dependence and abuse later in life [6,20]. In this study, we did not collect data on possible explanatory factors for the relationship between beha- vioural problems and cigarette smoking. Peer group pressure may play a role in children with delinquent