Young et al. BMC Public Health 2011, 11:874 http://www.biomedcentral.com/1471-2458/11/874 also have the opportunity to explore the interaction between individual religion and school denomination. Joiners Interpersonal Theory of Suicide Thomas Joiners Interpersonal Theory of Suicide (ITS) is arguably, the most comprehensive modern theory of sui- cide available and draws heavily on Durkheim’s concepts of anomie and alienation. The theory proposes that a lethal or near lethal suicide attempt requires the presence of three factors; thwarted belongingness (perceived loneli- ness or exclusion); perceived burdensomeness (perceived low self- or social-worth) and capability for suicide (past experience of or exposure to self-injury and suicide). The first factor, thwarted belongingness, is of primary rele- vance to this study and is broadly compatible with Dur- kheim’s concept of anomie. Thus, the present study fits well with both classic sociological and current psycholo- gical theories of suicide which emphases perceived social connection - the inverse of thwarted belongingness. Aims Using a large representative longitudinal sample of young people, surveyed in primary school and both dur- ing and after secondary school, we address three aims. First, to confirm if the significant associations between attempted suicide, suicide risk or self-harm and either school connectedness or school-level variables, found in prior studies, remain after adjustment for relevant indi- vidual level confounds; second, to explore the possible cross-level interaction between individual religion and school denomination suggested by both ET-M and Dur- kheim’s anomies theory; and third, to estimate what proportion of attempted suicide, suicide risk and self- harm can be attributed to the secondary school, an important ecological level within the ET-M and other theories relevant to suicidality. Methods The material for the study is drawn from the ‘West of Scotland 11 to 16/16+ Study’ [30], a longitudinal commu- nity health and lifestyle survey of young people, adminis- tered first in schools via questionnaire and then after leaving school by nurse interview. The focus here is on data collected in 1994-5, (age 11) 1999 (aged 15) and 2002-4 (age 19). The study received approval from Glas- gow University’s Ethics Committee, participating Educa- tion Authorities and schools. Informed consent was obtained from the parents of all participants via ‘opt-out’ consent forms at ages 11 and 15, oral consent from parti- cipants at each wave and written consent at age 19. Due to the school-based nature of the study, the sam- pling scheme involved several elements to ensure a repre- sentative sample at both the primary and secondary school stages and sufficient school units to explore Page 5 of 15 school effects using multilevel modelling methods [31]. Briefly, the survey used a reverse sampling procedure which randomly selected 43 secondary schools stratified by religious denomination and deprivation, with a sepa- rate stratum for independent vs. local authority run schools. These 43 secondary schools were used to select a random sample of 135 primary schools, comprising ‘feeder schools’, together with those making a high num- ber of placing requests. In contrast to some European or North American school systems, ‘feeder primary schools’ do not usually share a campus with a target secondary school, thus pupils from every primary school may be equally prone to experience some degree of school transi- tion problems [32]. From these primary schools, classes were randomly selected with all pupils in the classes eligi- ble to participate. Full details of the sampling strategy are available elsewhere [31]. Of 2793 target, pupils attending the 43 secondary schools, 2586 (93%) participated in the baseline (age 11) survey. At age 15, the number of partici- pants reduced to 2196 (79%), with losses in the post- school period reducing the sample size at age 19 to 1258 (45%). At age 15 1,860 (67%) respondents completed selected modules of a self-administered computerised (Voice) version of the Diagnostic Interview Schedule for Children (DISC) [33] which included a section on suici- dal thoughts and behaviours [34]. A section about cur- rent and previous self-harm was included in the nurse administered interview at age 19. At age 11, the sample was representative (in terms of sex and social class composition) of 11 year olds in the study area [35]. Differential attrition made later waves less representative, with attrition greater among lower social class groups, school truants, pupils of lower ability and with greater emotional and behavioural problems. To compensate for these biases, a weighting scheme was derived [35]. Use of these weights did not substantively alter the results and unweighted results are presented. The data used in this paper refer to 1,860 pupils who completed the psychiatric component and in their final year of compulsory education in 43 mainstream second- ary schools in the Glasgow area, 1256 of whom provided information when aged 19. Almost all parents provided information on pupils’ religious background and family socioeconomic status via a supplementary questionnaire in the baseline (age 11) of the study. After excluding those with missing data in other variables, 1698 cases were available for analysis of suicide risk at age 15, and 982 for self-harm at age 19. Due to low numbers, one school was omitted from the analysis. Measures Suicidality: attempted suicide, Suicide risk and self-harm As part of the 1999 (age 15) psychiatric interview, pupils were asked, ‘In the last year, was there a time when you