Mathematical Malpractice: Wisconsin Edition

Even Paul Krugmann has fallen for the canard that Wisconsin students, thanks to their unionized teachers, outperform everyone. Iowahawk above demonstrates that this is a result of mathematical malpractice — mostly failing to account for differences in testing regime and minority enrollment. Even the author of the studies Krugman references admits that the wrong point is being extracted from them, according to

At what point does continually presenting the wrong facts cross the line into deliberate deception?