Evaluating state tax revenue variability: a portfolio approach

This article develops a volatility model based on portfolio theory to examine state tax revenue variability. Unlike traditional parametric methods used to analyse state tax revenue variability, the portfolio approach allows the computation of a tax's share of total tax revenue that minimizes the overall variability in total state tax revenue given a state's portfolio of tax revenue sources. The model can thus be used to evaluate how closely a state's revenue portfolio is constructed to minimize variability in total state tax revenue. An empirical application of the model is conducted on a sample of US states. The volatility model presented here serves as a useful complement to parametric techniques that have been used to estimate tax revenue variability.