Association of Early-Life Exposure to Income Inequality With Bullying in Adolescence in 40 Countries.

Importance: While the association between income inequality and interpersonal violence has been attributed to the psychosocial effects of inequality (eg, increased class anxiety, reduced social capital), longitudinal evidence for this pathway is limited by a reliance on small ecological studies and cross-sectional data. The developmental consequences of early-life inequality for subsequent involvement in violence have not been investigated.

Objective: To examine the association between income inequality during infancy and early childhood and adolescents' involvement in bullying others, experiences of being bullied, or both.

Design, Setting, and Participants: The Health Behavior in School-aged Children survey study was conducted in European and North American schools. This analysis used individual data on bullying (being bullied, bullying others, or both) from 6 consecutive school-based surveys of 11-year-old to 15-year-old students carried out in 40 countries between February 1994 to March 2014. Data analysis occurred from March 2018 to January 2019.

Exposure: National Gini indices of income inequality for every year of life spanning a 35-year period (1979 to 2014).

Main Outcomes and Measures: Being bullied, bullying others, and both outcomes were measured using a common definition and questions adapted from the Bully-Victim Questionnaire and translated to many languages.

Results: The sample included 425 938 male students and 448 265 female students from 162 country-survey year groups in 29 196 schools. Linear regression coefficients indicated that early-life income inequality from birth to 4 years was positively associated with being bullied (male students: linear regression coefficient, 18.26 [95% CI, 11.04-25.47]; P < .001; female students: linear regression coefficient, 15.67 [95% CI, 10.02-21.33]; P < .001), and dual involvement in being bullied and bullying others (male students: linear regression coefficient, 5.55 [95% CI, 2.67-8.44]; P < .001; female students: linear regression coefficient, 2.45 [95% CI, 0.93-3.97]; P < .001), after differences in lifetime mean income inequality (from birth to when bullying was measured), national per capita income, family socioeconomic position, age, and cohort were controlled. No such association was found with bullying others after differences in being bullied were controlled.

Conclusions and Relevance: Being bullied is associated with early-life exposure to income inequality. Although further research on the underlying pathways is needed to guide intervention, these results suggest temporality in the association between inequality and violence and suggest that growing up in areas of high income inequality is associated with victimization in adolescence.