Research Database

People are enjoying longer retirement periods, and population growth is slowing and, in some countries, falling. In this article, we determine the implications of these demographic changes for the needed amount of government debt. If tax rates and the transfer share of gross national income (GNI) are both high, the needed debt is near zero. With such a system, however, huge deadweight losses are incurred as a result of the high tax rate on labor income. With a savings system, a large government debt to annual GNI ratio is needed. In a country with early retirement and no population growth, the needed government debt is as large as five times GNI, and welfare is as much as 24 percent higher in terms of lifetime consumption equivalents in the savings system relative to the tax-and-transfer system.

This paper is a case study of the use of vector autoregression (VAR) models to test economic theories. It focuses on the work of Christopher A. Sims, who in 1980 found that relationships in economic data generated by a small VAR model were inconsistent with those implied by a simple form of monetarist theory. The paper describes the work of researchers who criticized Sims' results as not robust and Sims' response to these critics. The paper reexamines all of this work by estimating hundreds of variations of Sims' model. The paper concludes that both Sims and his critics are right: Sims' conclusion about monetarism is robust, but some of his other statistical results are not. In general, the paper concludes that VAR models can be used to test theories, but that any relationships they uncover in the data must be carefully checked for robustness.