Straus adduced evidence for the view that exposure to parental corporal punishment increases the risk of aggressive conduct in children and adolescents. Straus's findings have been contested by Larzelere and Baumrind. A meta-analysis of the vast literature on corporal punishment, however, indicates that corporal punishment is related to poorer outcomes in children and youth. The methodologically soundest studies indicate "positive, moderately sized associations between parental corporal punishment and children’s aggression." Gershoff found that the trajectory of mean effect sizes (the size of the effect of corporal punishment on children's problem behavior) was curvilinear with the largest mean effect size in middle school ("M" = 0.55; on average the mean of corporal punishment group was more than half a standard deviation higher than the mean of the non-punishment group) and slightly smaller effect sizes in elementary school ("M" = 0.43) and high school ("M" = 0.45).