Richard Cebula and Edgar Feige "America's Underground Economy: Measuring the Size, Growth and Determinants of Income Tax Evasion in the U.S" requirements.
Accesat în 14 iunie 2012.  ^ Cebula, Richard; Feige, Edgar L. (n.d.). „America's Underground Economy: Measuring the Size, Growth and Determinants of Income Tax Evasion in the U.S”.