While he has contributed research to the fields of insurance, real estate and equity investments, he is probably best known as a vocal critic of the efficient market hypothesis and the Capital Asset Pricing Model (CAPM).
With his former professor, A. James Heins, he discovered in the late 60s and early 70s that, contrary to the prevailing theory, low risk stocks actually produce higher returns.
The resulting article bestowed on him the unofficial designation of "father of low volatility investing".
He was vocal concerning the evidence supporting market inefficiency and documented the low volatility anomaly and other quantitative factors such as value and momentum.
Based on articles published in the top academic journals in financial economics, Haugen has been ranked as the 17th most prolific researcher in finance.