A logistic growth theory of public expenditures: A study of five countries over 100 years

This paper offers a new theory and empirical testing of long-term trends of public expenditures for five countries. While Wagner’s Law would imply an exponential growth process of the ratio between public expenditures and national income (G/Y), the law should be rejected both on theoretical and empirical grounds, because it disregards the role of ever increasing distortionary taxation. However, under some conditions, the combination of Wagner’s Law and the Pigou’s conjecture that the excess burden of taxation constrains the growth of public expenditures can be captured by a non-linear first order differential equation. The equation is the Verhulst’s logistic, originally invented to model Malthusian predictions on population growth. The integration of a Verhulst equation generates an S-shaped curve. This analytical framework combines intuitions from a welfare economics and a public choice perspective, and potentially offers a new research strategy on the dynamics of government expenditures. We offer preliminary econometric estimates on long run trends (around 1870–1990) of G/Y in U.S., U.K., France, Germany, Italy. These estimates confirm a pattern of similar trajectories, in spite of different national parameters, and suggest that the logistic view of growth of government is consistent with observed data.