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One of the things I was concerned with when I went into trading was whether if trading principles can stand up to the scrutiny of statistical validity; I found comfort in this book as Grimes has conducted a lot of research with massive data behind his principles. It is easy to understand, and chock-full with tons of valuable information.
What I like about the book is that Grimes is willing to confront the issue of "efficient market hypothesis" (an academic theory that you cannot beat the market) head on, with his unique insights. It's been said that finding the unique combination of a good trader and a good teacher is nearly impossible, and I have found it in this book.
As one of the posters said below, this book will eventually join the tomes of trading "must reads"... I highly, highly recommend that you grab it!