Common pattern, just particularly clear in this case. But also happens for, say, Headstart intervention.https://twitter.com/ericgeller/status/926525187046199299 …
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It is a large, pre-specified government paid study with multiple year follow-up, not just 1. It's essentially as good as it gets.
Hell, simply getting the kids out of the mother/gparent's hair so they can make more money might have downstream effects.
Effects on behavior/attitudes important for life success may not be apparent in elementary school metrics.
It's as good as it gets, but it still covers only the short term. Long-term studies may be less well controlled, but they're not nothing.
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