To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jfineco.2004.03.008 Byline: Eric Ghysels (a), Pedro Santa-Clara (b), Rossen Valkanov (b) Abstract: This paper studies the intertemporal relation between the conditional mean and the conditional variance of the aggregate stock market return. We introduce a new estimator that forecasts monthly variance with past daily squared returns, the mixed data sampling (or MIDAS) approach. Using MIDAS, we find a significantly positive relation between risk and return in the stock market. This finding is robust in subsamples, to asymmetric specifications of the variance process and to controlling for variables associated with the business cycle. We compare the MIDAS results with tests of the intertemporal capital asset pricing model based on alternative conditional variance specifications and explain the conflicting results in the literature. Finally, we offer new insights about the dynamics of conditional variance. Author Affiliation: (a) Kenan-Flagler Business School, McColl Building, Suite 4100, University of North Carolina, Chapel Hill NC 27599-3490, USA (b) The John E. Anderson Graduate School of Management, University of California at Los Angeles, Los Angeles, CA 90095-1481, USA Article Note: (footnote) [star] We thank Michael Brandt, Tim Bollerslev, Mike Chernov, Rob Engle, Shingo Goto, Amit Goyal, Campbell Harvey, David Hendry, Francis Longstaff, Nour Meddahi, Eric Renault, Matt Richardson, Neil Shephard, and seminar participants at Barclays Global Investors, Centro de Estudios Monetarios y Financieros (Madrid), Emory University, the Global Association of Risk Professionals, Instituto Tecnologico Autonomo de Mexico (Mexico City), Instituto Superior de Ciencias do Trabalho e da Empresa (Lisbon), the Centre Interuniversitaire de Recherche en Analyse des Organisations Conference on Financial Econometrics (Montreal), Lehman Brothers, London School of Economics, Morgan Stanley, New York University, Oxford University, University of Cyprus, University of North Carolina, and University of Southern California for helpful comments. We especially thank an anonymous referee whose suggestions greatly improved the paper. Arthur Sinko provided able research assistance.