This is an important one, of interest to anyone involved in education. It urgently needs to be read by policy-makers. (Happily it seems to be doing the rounds, and comes via +Izabella Laba , +Qiaochu Yuan , +David Roberts, +Willie Wong , and others.)

Value Added Modelling (VAM) is a way to judge the effectiveness of school teachers. Or at least it is meant to be. It is used in New York state, among other places, and - this needs to be stressed - teachers' VAM scores genuinely effect their careers in terms of promotion, retention, bonuses, etc. (And that's before they get savaged in the press for being 'New York's Worst Teacher': )

So, what exactly does VAM measure? The short answer, as provided by Gary Rubinstein in a brilliant series of blog-posts where he crunches the New York VAM statistics, is nothing whatsoever.

Read them, pass them on.

Part 1:

Part 2:

Part 3:
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