Did What Works on Wall Street Stop Working?

James P. O’Shaughnessy’s What Works on Wall Street has long been one of my favorite books on investing. Not because it’s so readable—it includes pages and pages of backtests that are a real slog to get through. And not because it’s impeccable—there are some odd omissions, which I’ll get to later. And not because it strikes an estimable balance—there’s simply not enough about accounting measures, and what’s there is somewhat weak. . . .