From the article: > many participants had dropped out of the study since it began, a factor that affects all longitudinal studies. “We do lose more of those wi

From the article: > many participants had dropped out of the study since it began, a factor that affects all longitudinal studies. “We do lose more of those with higher conduct problems,” she said. "conduct problems" here refers to the bullies. they acknowledge the bias but I don't think they corrected for it.