Examining the Volatility of Ireland’s Tax Base in the Paradigm of Modern Portfolio Theory

  • Keith Fitzgerald Parliamentary Budget Office, Dublin
  • Jacopo Bedogni Parliamentary Budget Office, Dublin


This paper extends a theoretical and empirical framework commonly applied in international finance to present an alternative paradigm within which issues of tax revenue volatility in Ireland can be studied. We establish a trade-off between revenue growth and volatility, typically associated with financial asset returns. We observe strong but time-varying cointegration among tax revenue streams. Statistical tests of mean-variance spanning suggest diversification benefits from holding Income Tax and Excise Duty. We establish the minimum variance tax portfolio, and also find that, from a meanvariance optimality perspective, the portfolio consisting of 2017 tax shares is sub-optimal. Practical policy implications are discussed.