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Since Christopher Sims's "Macroeconomics and Reality" (1980), macroeconomists have used structural VARs, or Vector AutoRegressions, for policy analysis. Constructing the impulse-response functions and variance decompositions that are central to this literature requires factoring the variance-covariance matrix of innovations from the VAR. This paper presents evidence consistent with the hypothesis that at least some elements of this matrix are infinite for one monetary VAR, as the innovations have stable, non-Gaussian distributions, with characteristic exponents ranging from 1.5504 to 1.7734 according to ML estimates. Hence, Cholesky and other factorizations that would normally be used to identify structural residuals from the VAR are impossible.
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