alt Hacker NewsThe article explicitly calls out selection bias (this is entirely based on 90% that opted into using the tutor, there was no control group), I wish the headline did as well. "Engaged students score 0.71 - 1.30 SD better in tests" sounds like a much simpler explanation.
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tfirst • yesterday at 9:54 PM
"Full dosage of the Phosphor material is associated with an increase in final exam performance."
This sentence is accurate, but inevitably leads to the confusion you see in these comments.
I used to TA a graduate level CS math class at Georgia Tech. We regularly saw that the students who self-organized study groups did dramatically better in the course than average. One semester they told us to put everyone in study groups to see if it helped. The effect disappeared. Turns out that it was the self-selection of the most engaged students into a small group that mattered, not the study group itself.