William J. Bernstein is an American financial theorist. He is known for his research in the field of modern portfolio theory and for his self-help finance books for individual investors who wish to manage their own equity portfolios. He lives in North Bend, Oregon.
Bernstein is a proponent of the equity or index allocation school of thought, believing that all equity selection strategies should be focused on allocating between asset classes, rather than selecting individual stocks and bonds, or from the timing of their sales. Bernstein's first book, The Intelligent Asset Allocator, makes this case in detail; his second book, The Four Pillars of Investing: Lessons for Building a Winning Portfolio (McGraw-Hill, 2002; ISBN 0071385290), is aimed for those less comfortable with statistical thought. It also puts asset-class returns into long-term historical perspective.
Bernstein is a proponent of modern portfolio theory, which stands in stark contrast to the view that skilled managers can succeed in picking particular investments that will outperform the market, whether through market timing, momentum investing, or finding assets whose future value have been underestimated by the market. He argues that the financial research literature shows that most return is determined by the asset allocation of the portfolio rather than by asset selection.
Bernstein's third book, The Birth of Plenty, is a history of the world's standard of living; it proposes four conditions that have historically been necessary for it to rise. His fourth book, A Splendid Exchange: How Trade Shaped the World, published in April 2008 by Grove Atlantic, is a history of trade.
Bernstein holds a PhD in chemistry and an MD; he practiced neurology until retiring from the field.