Centre for Finance, Credit and Macroeconomics (CFCM)

CFCM 13/07: Fiscal rules and the maximum sustainable size of the public debt in the Diamond overlapping generations model


We show that the size of the maximum sustainable public debt in the Diamond (1965) OLG model depends on the choice of fiscal instrument. If tax revenue is exogenous, there is a maximum at an interior or bifurcation point, as in Rankin and Roffia’s (2003) initial paper but at a generally higher level than for their case of an exogenous debt. Conversely, if income tax rates are exogenous, the technical maximum is at a corner-point of degeneracy, provided the first Inada condition holds. However, as this implies notional average taxes of 100%, a Laffer Curve becomes important, giving rise to another concept of the maximum debt. More generally, for this closed economy case, the form of the production function in conjunction with the fiscal rule will determine whether the maximum debt is reached at a technical point of bifurcation or at a more behavioural one where tax payers en masse deny further payments to bond holders.

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Mark Roberts


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Posted on Sunday 1st September 2013

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