Reliability and validity of the Japan Ijime Scale and estimated prevalence of bullying among 4th through 9th graders: a large‐scale school‐based survey

AIM: The present study aimed at developing a novel scale, the Japan Ijime Scale (JaIS), to measure bullying in Japan with substantial reliability and validity, with which we estimated the prevalence of bullying among children and adolescents of school age. METHODS: The JaIS is a self-report questionnaire and consists of three parts: subscales measuring victimization and witnessing, and an item measuring perpetration. To test the reliability and validity of the two subscales, the authors analyzed responses to the JaIS from 2334 school students (Grades 4-9) in six elementary and three junior high schools in a middle-sized industrial city in central Japan, using exploratory factor analysis, item response theory, and examination of the external validity of the items. The prevalence of bullying victimization, witnessing, and perpetration was estimated. RESULTS: Item response theory models revealed that both the Victimization and Witness subscales have sufficient discrimination power and measurement precision, and the external validity of each scale has been confirmed. Using the JaIS, we found that 35.8% of students had been victims of bullying every 2-3 months (27.6% were solely victims and 8.3% were bully/victims), 32.8% had witnessed some type of bullying act, and 11.8% had perpetrated some type of bullying (3.5% as perpetrators, and 8.3% as bully/victims). CONCLUSION: The JaIS is a reliable and valid measure. Using this scale, we found a high prevalence of bullying victimization in Japanese schools.