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Does Joel Greenblatt's “Magic Formula Investing” really beat the market?
While it is true that this formula may have historically outperformed the market you have to keep one important thing in mind: once the formula is out in the open, the market inefficiency will disappear. Here is what I mean. Historically there have always been various inefficiencies in the market structure. Some people were able to find these and make good money off them. Invariably these people tend to write books about how they did it. What happens next is that lots of people get in on the game and now you have lots of buyers going after positions that used to be under-priced, raising demand and thus prices for these positions. This is how inter-exchange arbitrage disappeared. Its how high frequency trading is running itself into the ground. If enough demand is generated for an inefficiency, the said inefficiency disappears or the gains get so small that you can only make money off it with large amounts of capital. Keep in mind, as Graham said, there is no silver bullet in the stock market since you do not hold any data that is unavailable to everyone else.