TAX DATA FOR WEALTH CONCENTRATION ANALYSIS: AN APPLICATION TO SPANISH WEALTH TAX

As recent studies in different countries show, tax data offer the opportunity to estimate income or wealth shares for the upper income groups. However, several critical points must be considered in order to avoid misleading conclusions: the interpolation technique used, legal amendments, and tax fraud. In this note we take Spanish wealth tax as a case study to assess the importance of these factors, and compare our results with those obtained by Alvaredo and Saez (2009 ). Although the results of the two analyses are very similar, our approach complements theirs by offering a more precise treatment of the correction of fiscal underassessment and tax fraud in real estate, which is the main asset in Spaniards' portfolios.