By Nestor Lopez-Duran PhD
Research has consistently shown that the consequences of bullying are severe and range from impaired academic performance to increased risk for suicide. A smaller, but not less influential, line of research has examined the association between severe psychotic disorders (for example schizophrenia) and history of abuse. This research has shown that adults who experience psychotic disorder are more likely than non-affected adults to have a history of childhood trauma, including peer victimization. Could this mean that bullying may increase the risk for developing schizophrenia?
One way to start to examine this question would be to explore whether childhood victimization predicts the presence of early signs of psychotic disorders. This is the strategy employed by a team of British researchers who published their findings in this months issue of the prestigious Archives of General Psychiatry. This population-based study examined over 6,000 children at the ages of 8, 10, and 12 who were participating in a longitudinal study of human development in England. The authors measured the history of victimization at age 8 and 10 as predictors of psychotic symptoms at age 12. Psychotic symptoms included the presence of hallucinations (e.g., seeing or hearing things that are not there) or delusions (e.g., believing that people can read you thoughts).
- How common is bullying? 2,823 children, or 46% of the sample reported experiencing some type of bullying. 14% of the sample reported chronic victimization.
- Being victimized during middle childhood doubled the risk of experiencing definite psychotic symptoms in early adolescence (OR 1.94).
- The frequency of bullying was a key predictor of psychotic symptoms. Specifically, experiencing chronic bullying increased the risk of having psychotic symptoms by 252%.
- The type of bullying also played a role. While all types of bullying predicted an increase in the risk for psychotic symptoms, experiencing overt victimization (being beaten) combined with experiencing relational victimization (social exclusion, spreading rumors, etc) increased the risk of psychotic symptoms by 360% when compared to those who did not experience victimization.
- These findings remained stable after controlling for a number of potential explanatory variables, such as prior psychopathology, family adversity, and IQ.
Do these results indicate that victimization cause psychotic symptoms? No. The results are consistent with the hypothesis that victimization may lead to psychotic symptoms, but the nature of the study prevents us from making statements about causation. Although we use the terms increase the risk for developing x, this terminology is actually statistical terminology that refers to the probability for finding a specific outcome at a specific time. For example, in regards to the finding #2, being victimized in middle childhood increased the probability that the child would have psychotic symptoms at age 12. This does not address the question of why or how such probability is increased.
The authors correctly discussed this issue. Specifically, there is the possibility that children who were on path to developing psychotic disorders also engaged in behaviors during early childhood that made them more likely to be victims of bullying. In such a case, being victimized does not cause the psychotic symptoms. Instead, being victimized may have been the result of factors (such as extreme shyness) associated with later development of psychotic symptoms.
However, it is interesting that the authors found a dose response. That is, the more bullying the child experienced the higher the possibility of experiencing psychotic symptoms. Although one could argue that those at greater risk for developing psychotic symptoms elicited more frequent and severe bullying episodes, dose response effects are usually observed mostly in situations whether the predictor (in this case bullying) has a causative role in the outcome (psychotic symptoms). So this dose effect supports the notion that peer victimization may contribute to the development of psychotic symptoms in childhood and adolescence.
The reference: Schreier, A., Wolke, D., Thomas, K., Horwood, J., Hollis, C., Gunnell, D., Lewis, G., Thompson, A., Zammit, S., Duffy, L., Salvi, G., & Harrison, G. (2009). Prospective Study of Peer Victimization in Childhood and Psychotic Symptoms in a Nonclinical Population at Age 12 Years Archives of General Psychiatry, 66 (5), 527-536 DOI: 10.1001/archgenpsychiatry.2009.23