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But the datasets gathered in this way have been tiny — typically 20 people playing a handful of puzzles. Now one researcher has taken a different approach by mining the data from websites in which people can play games such as Sudoku. That's given him data on the way hundreds of players solve over 2000 puzzles, a vast increase over previous datasets and this has allowed him to plot the average time it takes to finish different puzzles. One way to assess the difficulty of Sudoku puzzle is in the complexity of each step required to solve it. But the new work suggests that another factor is important too — whether the steps are independent and so can be attempted in parallel or whether the steps are dependent and so must be tried in sequence, one after the other. A new model of this puzzle-solving process accurately reproduces the time it takes real humans to finish the problems and that makes it possible to accurately predict the difficulty of a puzzle in advance for the first time. It also opens the way for other studies of human problem solving using the vast datasets that have been collected over the web. Indeed work has already begun on the Sudoku-like puzzle game, Nurikabe."
Chartier uses two methods. One is the Colley Method, named after astrophysicist Wesley Colley who developed a method used by the BCS for college football (PDF). His basketball method only counts wins and losses, not margin of victory. The other method is the Massey method created by sports statistician Kenneth Massey (PDF), which does integrate scores. Chartier has not been banned from any office pools — at least none that he knows of. But as a result of coming pretty darn close to filling out a perfect bracket just by crunching the numbers, brackets have become a labor of love. 'Now that the brackets are actually out, I've had students in and out of my office all week, sharing new ideas,' says Chartier. 'For me, that's more fun than filling out a bracket. They will all be filling out brackets, so it's like I'm doing parallel processing. I know what might work, but watching them figure out the odds, is a thrill.'"