(British Medical Journal Specialty Journals) -- Adolescents who either witness or are victims of violence are prone to post traumatic stress disorder and depression, finds research in Injury Prevention.

The study was carried out in South Africa, where 60 deaths in every 100,000 are murders - 10 times the rate in the USA. Four private high schools in Cape Town took part in a survey, and 104 students responded to a questionnaire on violence.

Questions were grouped according to whether the student had witnessed or been the victim of violence at home - "known violence" - or in the larger community - "stranger violence." Respondents were also asked to report a range of symptoms that reflected post traumatic disorder and/or depression.

Over 80 per cent of respondents had either witnessed or been the victim of stranger violence. Over 70 per cent had either witnessed or been the victim of violence in the home. Exposure to one type of violence increased the risk of exposure to another type.

Almost 6 per cent of the sample surveyed met the criteria for post traumatic stress disorder, with one in five adolescents experiencing more than half the diagnostic symptoms. Depression was also associated with all types of violence.

The authors conclude that the levels of violence in children's homes and communities are far too high, putting them at risk of potentially serious mental health problems.

A second study from the USA shows that almost one in two male adolescents who had been involved in a fight in the preceding 12 months had injured others. Almost one in five had themselves been injured while fighting over the previous year.

A representative sample of over 1300 male adolescents from grades 7 to 12 took part in the research. All the boys had been involved in fights. Students who were involved in group fighting, who carried weapons, or who fought with strangers were significantly more likely to be injured.