Most acts of physical violence against children are undertaken with the intent to punish. In the United States, interviews with parents reveal that as many as two thirds of documented instances of physical abuse begin as acts of corporal punishment meant to correct a child's behavior, while a large-scale Canadian study found that three quarters of substantiated cases of physical abuse of children have occurred within the context of physical punishment. Other studies have shown that children and infants who are spanked by parents are several times more likely to be severely assaulted by their parents or suffer an injury requiring medical attention. Studies indicate that such abusive treatment often involves parents attributing conflict to their child's willfulness or rejection, as well as "coercive family dynamics and conditioned emotional responses". Factors involved in the escalation of ordinary physical punishment by parents into confirmed child abuse may be the punishing parent's inability to control their anger or judge their own strength, and the parent being unaware of the child's physical vulnerabilities.