Scott links to this study, which is more convincing. They measure the difference between “physical mild (slap, spank)” and “physical harsh (use weapon, punch, kick)” punishment, with ~10% of children in the latter category. They consider children of twins to control for genetic confounders, and find something like a 0.2 SD effect on measures of behavioral problems at age 25. There is still confounding (e.g. households where parents beat their kids may be worse in other ways), and the effects are smaller and for rarer forms of punishment, but it is getting somewhere.
It’s my strong impression that parents are more likely to use harsh punishment when they themselves are more stressed and overwhelmed. I expect this to be a big confounder.
Scott links to this study, which is more convincing. They measure the difference between “physical mild (slap, spank)” and “physical harsh (use weapon, punch, kick)” punishment, with ~10% of children in the latter category. They consider children of twins to control for genetic confounders, and find something like a 0.2 SD effect on measures of behavioral problems at age 25. There is still confounding (e.g. households where parents beat their kids may be worse in other ways), and the effects are smaller and for rarer forms of punishment, but it is getting somewhere.
It’s my strong impression that parents are more likely to use harsh punishment when they themselves are more stressed and overwhelmed. I expect this to be a big confounder.