Partialling out, what a multiple-regression coefficient means
Asked at DE Shaw
People say a multiple-regression coefficient measures the effect of one predictor "holding the others constant," but what does that mean mechanically?
State the Frisch–Waugh–Lovell result and use it to explain why controlling for variables changes a coefficient.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.