Using confidential tax shelter and tax return data obtained from the Internal Revenue Service, this study develops and validates an expanded model for inferring the likelihood that a firm engages in a tax shelter. Results show that tax shelter likelihood is positively related to subsidiaries located in tax havens, foreign-source income, inconsistent book-tax treatment, litigation losses, use of promoters, profitability, and size, and negatively related to leverage. Supplemental tests show that total book-tax differences (BTDs) and the contingent tax liability reserve are significantly related to tax shelter usage, while discretionary permanent BTDs and long-run cash effective tax rates are not. Finally, the model is weaker, yet still significant, in the FIN 48 disclosure environment. This research provides investors and policymakers with an extended, validated measure to calculate the presence of extreme cases of corporate tax aggressiveness. Such information could also aid analysts and other tax and non-tax researchers in assessing the benefits and risks of firm behavior.

We examine whether public disclosures of tax reserves recently made available through Financial Interpretation No. 48 (FIN 48) reflect corporate tax shelter activities. Understanding this relation is important to corporate stakeholders and researchers keen to infer the aggressive nature of a firm's tax positions from its tax reserve accrual. Our study links public disclosures of tax reserves with mandatory private disclosures of tax shelter participation as made to the Internal Revenue Service's Office of Tax Shelter Analysis. We find strong, robust evidence that the tax reserve is positively associated with tax shelters, while other commonly used measures of tax avoidance are not. Based on out‐of‐sample tests, we also show that the reserve is a suitable summary measure for predicting tax shelters. The tax benefits of tax shelters are economically significant, accounting for up to 48% of the aggregate FIN 48 tax reserves in our sample.

Using confidential data from the Internal Revenue Service on who signs a corporation's tax return, we investigate whether the party primarily responsible for the tax compliance function of the firm—the auditor, an external non-auditor, or the internal tax department—is related to the corporation's tax aggressiveness. We report three key findings: (1) firms preparing their own tax returns or hiring a non-auditor claim more aggressive tax positions than firms using their auditor as the tax preparer; (2) auditor-provided tax services are related to tax aggressiveness even after considering tax preparer identity, which supports and extends prior research using tax fees as a proxy for tax planning; and (3) Big 4 tax preparers, in particular, are linked to less tax aggressiveness when they are the auditor than when they are not the auditor. Our findings help policymakers and researchers better understand an important feature of tax compliance intermediaries; particularly, how the dual role via audits is related to observable corporate tax outcomes.

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