I explain what I've learned from creating and judging thousands of predictions on personal and real-world matters: the challenges of maintenance, the limitations of prediction markets, the interesting applications to my other essays, skepticism about pundits and unreflective persons' opinions, my own biases like optimism & planning fallacy, 3 very useful heuristics/approaches, and the costs of these activities in general.
Plus an extremely geeky parody of Fate/Stay Night.
This essay exists as a large section of my page on predictions markets on gwern.net
: http://www.gwern.net/Prediction%20markets#1001-predictionbook-nights
True, of course in Krugman's case I suspect most of his predictions amounted to predicting that the financial crisis was going to be really but, and thus were also correlated.
Another LW discussion of Krugman's alleged accuracy pointed both here and to a spreadsheet with the actual predictions. About half of his predictions did indeed amount to saying that the financial crisis was going to be really bad. There were some political ones too but they weren't of the "my team will win" form, and he did well on those as well.