The Tax Gap: A Methodological Review

The global economic crisis has highlighted the continuing problem of tax evasion. For tax agencies to respond, an important antecedent necessitates knowing the extent of the problem. This study is the first to comprehensively review recent research on the tax gap. Our primary contributions are two-fold. First we argue that the tax gap, as conventionally defined, is conceptually flawed because it fails to capture behavioral responses by taxpayers adequately. Our second contribution is to review methods for measuring the tax gap and compare empirical estimates. We suggest that many of the most trenchant criticisms of conventional tax gap measurement (and the ‘hidden economy’ measures that underlie them) leave only microdata-based measures of tax non-compliance as likely to deliver more reliable tax gap estimates. Even here, however, further work is required, on both conceptual and empirical aspects, before tax gaps suitable for policy analysis (e.g. implications for enforcement policy) are likely to be delivered.