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Asset Pricing with a Factor Arch Covariance Structure: Empirical Estimates for Treasury Bills


  • Robert F. Engle
  • Victor Ng
  • Michael Rothschild


Asset pricing relations are developed for a vector of assets with a time varying covariance structure. Assuming that the eigenvectors are constant but the eigenvalues changing, both the Capital Asset Pricing Model and the Arbitrage Pricing Theory suggest the same testable implication: the time varying part of risk premia are proportional to the time varying eigenvalues. Specifying the eigenvalues as general ARCH processes. the model is a multivariate Factor ARCH model. Univariate portfolios corresponding to the eigenvectors will have (time varying) risk premia proportional to their own (time varying) variance and can be estimated using the GARCH-M model. This structure is applied to monthly treasury bills from two to twelve months maturity and the value weighted NYSE returns index. The bills appear to have a single factor in the variance process and this factor is influenced or "caused in variance" by the stock returns.

Suggested Citation

  • Robert F. Engle & Victor Ng & Michael Rothschild, 1988. "Asset Pricing with a Factor Arch Covariance Structure: Empirical Estimates for Treasury Bills," NBER Technical Working Papers 0065, National Bureau of Economic Research, Inc.
  • Handle: RePEc:nbr:nberte:0065 Note: ME

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    1. Obstfeld, Maurice, 1981. "Capital Mobility and Devaluation in an Optimizing Model with Rational Expectations," American Economic Review, American Economic Association, vol. 71(2), pages 217-221, May.
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