Factors from Scratch:

The excess returns associated with Value and Momentum result from convergent and divergent processes, respectively. Value stocks are systematically underpriced and gradually converge on their fair value over time. Momentum stocks start out fairly valued or slightly overvalued, and go on to become more overvalued in the short-term, before reverting back. Both styles represent a market mistake that can be captured as alpha. In this piece, we're going to make all of these points more clear through a unified framework that we've developed to explain how factors work.