Investors - be they aggressive or conservative, self-directed or professionally managed - are always on the lookout for an edge. And in James O'Shaughnessy's What Works on Wall Street: A Guide to the Best-Performing Investment Strategies of All Time, they'll find a solid one: authoritative analysis of popular practices from the past. The author examines three decades of stock market data to show how 15 of the most common investment tactics have fared over time.