The big picture is: the main thing you should be concerned about in the future are incremental returns on capital going forward. As it turns out, past history of a good return on capital is a good proxy for this but obviously not foolproof. I think this is an area where thoughtful analysis can add value to any simple ranking/screening strategy such as the magic formula. When doing in depth analysis of companies, I care very much about long term earnings power, not necessarily so much about the volatility of that earnings power but about my certainty of "normal" earnings power over time.