Young et al. BMC Public Health 2011, 11:874 http://www.biomedcentral.com/1471-2458/11/874 resulting from fully adjusted (adjusted for all covariates) models. Depression at age 11 was associated with increased odds of attempted suicide and suicide-risk at age 15, but not self-harm at age 19. Use of psychiatric services at or before age 11 was associated with only age 15 suicide-risk (OR 2.28, p = 0.05), whereas victimisa- tion was unrelated to any outcome. Compared to Church of Scotland (Protestant) pupils, Catholic pupils had lower odds of attempted suicide (OR 0.39, p = 0.04), suicide-risk (OR 0.51, p = 0.08) at age 15 and of self-harm (OR 0.07, p = 0.001) at 19. After adjusting for all the variables in the model, perceptions of the local neighbourhood were not related to any of the outcomes. For all three outcomes, school (dis)engagement was associated with a 15-18% increase in odds for every SD above the average; significantly for suicide-risk (p = 0.006) and near significantly for attempted suicide (p = 0.055) at age 15. Poor school involvement was also asso- ciated with a similar, but non-significant (p = 0.077), increase in the odds of attempted suicide by age 15. A poor school rating was associated with a significant increase in the odds of suicide-risk by age 15 (OR 1.65, p = 0.016). In contrast to the findings for individual reli- gion, when compared to pupils attending a non-denomi- national school, those attending a denominational (Catholic) school had a substantial increase in the odds of attempting suicide (OR 2.24, p = 0.048), suicide-risk by age 15 (OR 1.89, p = 0.071), and self-harm by age 19 (OR 9.15, p = 0.003). Cross-level interactions The apparent paradoxical result that individual Catholic religion is a protective, but Catholic school attendance a risk factor, can be explained by examining their cross- level interaction. Table 6 shows the cross-tabulation between these two variables. Where there is a ‘mis- match’ between religion and denomination there is approximately a two to fourfold increase in the rates of attempted suicide, suicide-risk and self-harm and this is reflected in the univariate odds ratios (Tables 3, 4 and 5). Adding this ‘religious mismatch’ interaction to the adjusted model removed both the protective effect of individual (i.e. catholic advantage) religion and the increased risk associated with denominational school, Table 6 Relationship between individual religion, school denomination and attempted suicide, suicide-risk and self-harm Outcome Religion & school denomination Match% (N) Mismatch% (N) p Attempted suicide (age 15) 5.8 (95) Suicide risk (age 15) 9.1 (150) Self-harm (age 19) 6.5 (63) 14.5 (8) 16.4 (9) 22.2 (4) 0.016 0.070 0.029 Page 12 of 15 although in the fully adjusted model the interaction was not significant. To explore if this lack of significance for the interaction in the adjusted model was attributable to low statistical power, the analysis was repeated using standard multilevel regression with the ‘pseudo’ continu- ous suicidality score as the outcome; in that multivariate analysis the interaction was significant (p = 0.03, 1-tail). Excluding pupils from minority religion (Muslim, Jewish, Methodist, Baptist, etc.) made no substantive difference to results; therefore it is unlikely that our results are attributable to the influence of minority religions. School-level variance In line with previous studies of school and ‘wellbeing’ the estimated percent of variance attributable to school in the model was low - less than 1% for attempted suicide, 1.3% for suicide-risk, and 1.6% for self-harm and this altered little in the fully adjusted models. Discussion and Conclusions Returning to the first of our three aims, after adjusting for social background we found several significant asso- ciations between suicidality or self-harm and school connectedness (school engagement) and school-level (school denomination) variables. However, many asso- ciations were non-significant, although of broadly of similar effect size. In relation to our second aim, we found evidence for a cross-level interaction between individual religion and school denomination compatible with Durkheim’s theory of suicide. In relation to our final aim and in line with previous studies of ‘psycholo- gical wellbeing’, we found that very little of the variation in attempted suicide, suicide-risk or self-harm is attribu- table to the school level. If replicated, these findings have important implications for suicidology, school- based public health policy and interventions aimed at reducing youth suicide and self-harm, although we explore several alternative explanations for our findings. Several covariates behave differently in the adjusted models, only becoming significant in multivariate ana- lyses, most notably social class and religion/school denomination and this requires explanation. Unadjusted, social class seems largely unrelated to suicide-risk and self-injury, but the two are occasionally associated in the adjusted models. This is likely attributable, at least in part, to statistical artefact and the use of a relatively small reference group. Children from privileged back- grounds - social class I (doctors, lawyers, academics, etc.) appear to be at increased risk. While traditionally a low-risk group, children of high social class parents, especially females, may feel additional academic pressure during adolescence because of higher parental- and self- expectations [50]. In the unadjusted models, religious upbringing and the denomination of the school attended