Young et al. BMC Public Health 2011, 11:874 http://www.biomedcentral.com/1471-2458/11/874 thought seriously about killing yourself?’ and ‘Have you ever, in your whole life, tried to kill yourself or make a suicide attempt?’ A ‘yes’ response to either question was categorized as ‘suicide risk’ at age 15 and any report of an attempt to ‘kill yourself’ categorized as a ‘suicide attempt’(ever). The ‘nadir’ or highest risk model of suicide prediction has considerable empirical support [36]. Its main propo- sal is that the likelihood of an imminent suicide attempt is (to some degree) contingent on both past and recent suicidal thoughts and behaviors, and this risk increases as cognitions become more recent, concrete and goal directed, with prior experience of attempting suicide the highest risk. An age 15 ‘suicide risk’ score, range 0 (least risk) to 5 (most risk), was created using 5 binary items from the psychiatric assessment with each item ranked in term of ‘risk or likelihood of future attempted sui- cide’. Based on their responses to these five items, pupils were assigned the single highest risk score at age 15 from the following; no risk factor = 0; recent (last month) thoughts of death or dying = 1; suicidal ideation (last year) = 2; recent (last month) suicidal ideation = 3; planned a suicide (last year) = 4; suicide attempt (ever) = 5. Additional file 1 provides details of the exact ques- tions asked and risk score assigned to each item. The 2003 (age 19) nurse interview asked ‘Have you ever tried to hurt yourself or harm yourself deliberately’ and age at first act of self harm. Few (under 5%) reported self-harm before age 11, the majority (over 70%) of young people who self-harmed first did so during their secondary school years. Prior mental health risk At age 11, several indicators of early mental health pro- blems or risk were recorded. Levels of depression and anxiety were assessed using the 6-item Kandel and Davies Depression Scale [37]. To assess previous psy- chiatric and major mental health problems, parents were asked about use of psychiatric services in relation to their child. Bullying and victimisation are strongly asso- ciated with mental health and, at 11, pupils were asked two questions about being bullied and teased (5-point scale, never to everyday) [38]. Pupils bullied or teased on a regular basis (weekly or more frequently) were categorised as being victimised. Social and family background In addition to gender, several other demographic and social background factors were recorded. Relative age has been linked with suicide [39] and the relative age of each pupil compared to cohort average (15 years, 5 months) at age 15 was calculated in months. Social class, obtained at age 11, was based on information about the occupation of the head of household, derived primarily from parents themselves, or, in the absence of a parental questionnaire, from reports by their children, which we have found to Page 6 of 15 be reliable [40]. This was coded using the standard UK classification system [41] and categorized into social classes I-V, or missing. Although pupils reported parental social class at each study wave, social class was generally stable; accordingly, we include only baseline social class measures. At age 15 an area deprivation score, range 1 (least) to 7 (most deprived), was derived from pupils’ postal codes using the ‘Carstairs’ index [42]. Religious affiliation was obtained from parents at baseline and cate- gorized as Church of Scotland (Protestant - the majority religion and the established church in Scotland), Catholic (the second largest religion in Scotland), other (Muslim, Jewish, Methodist, Baptist, etc.), ‘none, atheist/agnostic’, or missing. At age 15, family structure was coded as 2- parent, 1-parent and other (reconstituted, other relative, foster parent, or other carer); low frequencies ruled out the creation of a separate ‘reconstituted’ (one ‘birth’ par- ent and new partner) category. Perception of the quality of parental-child relations was assessed using the 8-item Brief Parental Bonding Instrument (PBI-BC) [43], self- administered at age 15. The instrument is highly reliable (Cronbach’s alpha > 0.7 for each subscale), demonstrates considerable validity [44] and produces scores on two scales representing perceived parental care, e.g. ‘My par- ents help me as much as I need’ and control, e.g. ‘My parents treat me like a baby’; this mirrors the factor structure of the full scale. We used principal component (varimax) analysis of the 8 PBI-BC items to calculate fac- tor scores. This allowed us to simultaneously derive stan- dardized scores for interpretability, centre the scales and produce two uncorrelated measures; thereby reducing potential collinearity issues. Perception of local neighbourhood Pupils completed 11 questions relating to perceptions of their residential neighbourhood, derived from questions used in prior studies of environment influences used by the authors [45,46], or based on items used to evaluate school environment, broadly similar to Rutter’s ‘school ethos’ items [3], but adapted for neighbourhoods. These were rated on either 3-point (good, average or bad), or 4-point scales (strongly agree to strongly disagree). See Additional file 2 for details. Principal component (varimax) analysis of 11 items measuring perception of the local neighbourhood at age 15 produced three factors accounting for 57% of the variance. These were labelled neighbourhood cohesion, e. g. ‘I feel part of this area’; neighbourhood safety and inci- vilities, e.g. ‘I feel safe in this area’ and neighbourhood facilities, e.g. rating of ‘places for young people to meet’. See Additional file 2 for details. School connectedness and perceptions of school environment Pupils completed a series of questions related to aspects of school connectedness, including perceptions of the