But that's the whole point: the book is like a stock price. It reflects all available information. Across all gamblers, it should be pretty accurate/efficient.

But that's the whole point: the book is like a stock price. It reflects all available information. Across all gamblers, it should be pretty accurate/efficient. The reason I like this approach is that it doesn't rely on a model of winning percentage that some statistician somewhere threw together. Which would you trust more to reflect the true value of Google: some random Goldman analyst's model, or the price of GOOG?