Compute bias and variance

Problem

At a fixed input, the true value is f(x)=3f(x)=3, and noise is ignored. Across three training sets, model A predicts (1,1,1)(1,1,1) and model B predicts (1,3,5)(1,3,5). Using population variance, compute each model's bias, squared bias, variance, and expected squared error. Which model is better here?

Reveal answer or reference solution

Model A has mean 11, bias −2-2, squared bias 44, variance 00, and MSE 44. Model B has mean 33, bias 00, squared bias 00, variance

(1−3)2+0+(5−3)23=83,\frac{(1-3)^2+0+(5-3)^2}{3}=\frac{8}{3},

and MSE 83\frac{8}{3}. Model B is better here because 83<4\frac{8}{3}<4, though it varies more across training sets.

Outcome

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