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Introduction
Bullying occurs in all schools, but its relevance to health and wellbeing is uncertain. 1-3 On the one hand it can be considered a common and normal developmental experience; alternatively, it can be considered an important cause of stress and of physical and emotional problems. 4-6 A meta-analysis of studies investigating the relation between victimisation and psychosocial maladjustment found a stronger association with measures of depression than with anxiety, loneliness, or general self esteem. 1
Unfortunately, the cross sectional design of most studies precludes inferences about causality. The few available prospective studies have generally focused on primary school children before the early increase in depression in adolescence, 7 with the principal outcomes being school maladjustment, loneliness, and depression. 8-10 One small longitudinal study of adolescents found that high levels of victimisation predicted poor physical health for boys and girls and poor mental health for girls. 11 Olweus found that boys victimised between the ages of 12 and 16 had increased levels of depression as young adults; however, no adjustment was made for previous mental health states in this study. 5
We carried out a prospective study of secondary school students. The data derive from three waves of data collected from students involved in a randomised controlled trial of a school based intervention to promote the emotional wellbeing of young people. 12 Intervention effects in the trial are not the main focus of this paper. Data were collected at the beginning and end of year 8 (second year of secondary school, mean age 13 years) and 12 months later (end of year 9). Our aim was to use these prospective data to examine the relation between a history of victimisation (in year 8) and the incidence of self reported symptoms of anxiety or depression in year 9.
Methods
A cluster randomised controlled design was used for the allocation of education districts to intervention or control status. In metropolitan Melbourne, 12 districts were sampled with a probability proportional to the number of secondary schools (including government, independent, and Catholic schools) and were randomly allocated to intervention or control status. We used simple random sampling to select 12 schools from the "intervention" districts and 12 from the "control" districts. Six country schools were randomly drawn from two...