I believe it is a consequence of A) netflix evaluating the algorithms in terms of the squared error and B) different classification algorithms making different

I believe it is a consequence of A) netflix evaluating the algorithms in terms of the squared error and B) different classification algorithms making different types of mistakes. Take a simple example, with two movies (A and B), and two algorithms (X and Y). Say Alg. X rates movie A perfectly, but is off by 2 for movie B. Meanwhile, Alg. Y rates movie B perfectly, but is off by 2 for movie A. The squared errors for the different algorithms will be: Alg X: 4 (=0^2 + 2^2) Alg Y: 4 (=2^2 + 0^2) Mean of Alg X and Alg Y: 2 (=1^2 + 1^2)