This note is in response to some of the points raised in the Agnoff Lecture by Ed Haertel. The lecture makes two big points: 1) Teacher effectiveness ratings based on current Value Added Models are ‘unreliable.’ They are actually much worse than just unreliable; see below. 2) Simulated counterfactuals of

Selection biases in the participant pool generally have limited impact on inference. One way to estimate population treatment effect from effects estimated using biased samples is to check if treatment effect varies by ‘kinds of people’, and then weight the treatment effect to population marginals. So far so good. When