This paper contains many reasonable findings:
Kleven, Henrik Jacobsen, Martin B. Knudsen, Claus Thustrup Kreiner, Søren Pedersen, och Emmanuel Saez. "Unwilling or Unable to Cheat? Evidence From a Tax Audit Experiment in Denmark". Econometrica 79, nr 3 (2011): 651–92. Link

From the abstract (my emphasis)
using quasi-experimental variation created by large kinks in the income tax schedule, we find that marginal tax rates have a positive impact on tax evasion for self-reported income, but that this effect is small in comparison to legal avoidance and behavioral responses. Third, using the randomization of enforcement, we find that prior audits and threat-of-audit letters have significant effects on self-reported income, but no effect on third-party reported income. All these empirical results can be explained by extending the standard model of (rational) tax evasion to allow for the key distinction between self-reported and third-party reported income.