This is a huge study. Dr. Takizawa and his colleagues had investigated a total of seven thousand persons for 50 years to evaluate the influence of being bullied upon the mental state in later life of the victims.
American Journal of Psychiatry: Adult Health Outcomes of Childhood Bullying Victimization: Evidence From a Five-Decade Longitudinal British Birth Cohort
The results are to be predicted. Participants who were bullied in their childhood are more likely to be mentally ill later. The victims have approximately twice of risk for depression, anxiety disorder, and even suicide. The authors emphasize the need to prevention of bullying.
I was astonished with the fact that this research has been completed. It is hard to imagine how much time and money were spent for this cohort. I admire the researchers and participants.
By the way, it is a little strange that only three authors are specified in this article. I guess at least one hundred researchers were more or less engaged in this survey. Many more persons should be honored as the authors, even not all of them.
Unfortunately, it cannot be said that this research has proven that bullying is one of the causes of mental disorders. There is a difference between causal relationship and mutual relationship. People who were frequently bullied might have some characteristics that is possible to lead a mental disorder by nature. It is not sure whether they have not been suffering from mental illnesses if the victims had been protected from bullying. Nothing to say, it is ethically difficult to make an experiment about this matter.
In this study, some potential factors likely to affect the result, such as intelligence, were statistically adjusted in advance. However, it is impossible to identify all the factors intentionally.
This study suggests an ordinary thing: Bully is a bad habit. And the reliability of this finding is not adequately high. Nonetheless, I strongly respect the researchers who performed this study for their courage and patience.