A study including 6,437 early adolescents with an average age of 12.9 was carried out by Andrea Schreier, Ph.D., and his colleagues of The Warwick Medical School, University of Warwick, Coventry, England. The children participated in the Avon Longitudinal Study of Parents and Children (ALSPAC). Questionnaires were regularly sent by mail to parents concerning their child's physical condition and progress since birth. Beginning at the age of seven, the children were submitted to physical and psychological evaluations on a yearly basis.

During the yearly visits, they were rated by skilled interviewers on whether during the preceding six months they had experienced hallucinations, delusions, thought disorders or any other psychotic symptoms. Peer victimization is defined as harmful actions and unfair treatment by one or several other students with purpose to harm. Children, parents and teachers were required to account on whether the child had suffered such oppression.