CFCM 14/01: The maximum debt-GDP ratio and endogenous growth in the Diamond overlapping generations model: Three overlapping generations are better than two

Abstract

While the public debt has an interior maximum in the Diamond OLG model, due to an inherent nonlinearity [Rankin and Roffia (2003)], this feature also extends to a linear, AK model when it is conjoined with a backward-looking adjustment process for public debt [Braeuninger (2005)]. We show that if the debt dynamics are forward-looking, the maximum will instead be at a degeneracy – another possibility considered by Rankin and Roffia. However, the main point of the present paper is to show that any debt maximum in a finite-horizon model will be of an implausibly low order of magnitude, unless households save over at least two periods. This is because it is the debt flow that crowdsout investment flows, while this is synonymous with the debt stock in a model with only two, non-altruistic, overlapping generations, thus leading to a low maximum stock by default. Removing this restriction produces plausible results, and causes a low rate of economic growth to be a cause as well as a consequence of a high public debt.

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Authors

Mark Roberts

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