This kind of correlational study is awash in survivorship bias, and may not even apply to age cohorts born in a different society in a different era. Most likely, the study results neither show what is sufficient for a happy life for all nor what is necessary for a happy life for anyone. It would take an experimental study design with a study population more representative of the broad range of present-day people (no…
What if some children grow up in certain ways regardless of how they're raised, and this is what causes them to have shitty relationships with their parents? Maybe some kids don't get good parenting simply because they became little shits? And then this carried on into their lives?