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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That's one study of one-year effects. There are a number of studies showing positive long-term effects, eghttps://www.brookings.edu/research/the-long-term-impact-of-the-head-start-program/ …
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.
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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