Those twins studies constitutes a low-power measurement of effects of whatever it is that parents in the broad population happen to be doing during the time period of the study.

Wow, I never thought of it that way. Thanks

It should not be confused with a measurement of the effects of best practice.

Aren't twin studies best practice? What's better?

As a broad estimate, any intervention that health insurance will pay is such an evidence-based intervention and there are more outside of that category, the standard for which evidence-based intervention are cover vary from state to state, nation to nation. Some of these have long-term effects.

That's a useful hereustic. Thanks for making it so clear :)

You write "barring...trauma". Is the definition of "trauma" broad enough to capture all the evidence-based interventions?

I'm a little confused here.