The statistical relationship seems quite robust, but the analysis of causation is purely qualitative.
I am out of my depth assessing the psychological and historical evidence they cite, and it might well be true that kinship is an important component of it. However the usual standard for evidence in econometrics is a natural experiment, which they did not do.
FWIW I reviewed and redid the analysis in Heinrich’s paper.
https://forum.effectivealtruism.org/posts/wWGi4jTNNMhz2pHhJ/persistence-a-critical-review-abridged
The statistical relationship seems quite robust, but the analysis of causation is purely qualitative.
I am out of my depth assessing the psychological and historical evidence they cite, and it might well be true that kinship is an important component of it. However the usual standard for evidence in econometrics is a natural experiment, which they did not do.