What's next? There are still many interesting questions at the trait level. For example, heritability estimates for BMI vary substantially across methods and suggest that more complex environmental interactions may be at play (an echo of prior work: pubmed.ncbi.nlm.nih.gov/28692066/).

So there you have it, twin study estimates were greatly inflated, and molecular data sets the record straight. I walk through possible counter-arguments, but ultimately the uncomfortable truth is that genes contribute to traits much less than we always thought.

I think the general lessons are:

1. Be clear about your goal (_estimand_)

2. Be clear about your analytical method (_estimator_)

3. Be clear about the assumptions that connect method to goal (_design_)