In the latest edition of the In Practice series, Mark Harrison, CFA, and Phil Davis summarize recent research into whether buying US equities that are underpriced based on simple fundamental-to-price ratios yields better performance than investing in broad market indexes.
In the spirit of dumb alpha, we can say that simple trailing P/E ratios are far better value indicators than forward P/E ratios. Or as I tell my colleagues at work: Never ever use forward P/E ratios. Ever.