[NLips]

The research is pretty poor. The main problem is that all physical punishment is landed into a single pot, but there is clearly a world of difference slapping a fifteen year old in the face and slapping the bottom of a four year old.

See here for a useful meta-analysis: https://link.springer.com/article/10.1007/s10567-005-2340-z

[panic]

Many people who hit kids aren't making fine distinctions like that. The whole point of the research is to address the general practice.

[naasking]

If the general practice can be effective depending on fine distinctions, and if such fine distinctions exist, then they matter. General advice like given above is then just bad advice.