Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
This paper offers a new approach to estimating time-varying covariance matrices in the framework of the diagonal-vech version of the multivariate GARCH(1,1) model. Our method is numerically feasible for large-scale problems, produces positive semidefinite conditional covariance matrices, and does not impose unrealistic a priori restrictions. We provide an empirical application in the context of international stock markets, comparing the new estimator with a number of existing ones. © 2003 President and Fellows of Harvard College and the Massachusetts Institute of Technology.