The goal of this paper is to estimate time-varying covariance matrices. Since the covariance matrix of financial returns is known to change through time and is an essential ingredient in risk measurement, portfolio selection, and tests of asset pricing models, this is a very important problem in...

A well-known pitfall of Markowitz portfolio optimization is that the sample covariance matrix, which is a critical input, is very erroneous when there are many assets to choose from. If unchecked, this phenomenon skews the optimizer towards extreme weights that tend to perform poorly in the real...

The goal of this paper is to estimate time-varying covariance matrices. Since the covariance matrix of financial returns is known to change through time and is an essential ingredient in risk measurement, portfolio selection, and tests of asset pricing models, this is a very important problem in...

The central message of this paper is that nobody should be using the sample covariance matrix for the purpose of portfolio optimization. It contains estimation error of the kind most likely to perturb a mean-variance optimizer. In its place, we suggest using the matrix obtained from the sample...

Bei der Ansiedlung großflächiger Einzelhandelsvorhaben stellt sich stets die Frage nach ihrer Verträglichkeit. Zur Beantwortung dieser Frage sind Einzelhandelsgutachten unerlässlich. Dabei stehen die Ergebnisse und nicht zuletzt die Einzelhandelsgutachten selbst immer wieder in der Kritik,...