Bypassing progressive taxation: fraud and base erosion in the Spanish income tax (1970-2001)

In this paper I estimate under-assessment of incomes in the Personal Income Tax during the years following its introduction in Spain. The methodology combines an analysis of discrepancy with National Accounts and an econometric exercise, which follows and slightly modifies the Feldman and Slemrod (2007) procedure, based on the relation of reported charitable donations with the composition of income in tax micro-data. Both calculations show that concealment of income differed substantially across sources and levels, with better compliance at the bottom of the distribution of taxpayers. Because of this, fraud made the tax less progressive than it was on paper. Compliance improved over the next decades, but the overall levels were still far from those attained in developed countries, because of lack of administrative capacity or political will to enforce the new regulation. In this way, general, comprehensive income taxation was hardly a reality 20 years after its introduction.