The data form the national sources follow the classification recommended by the 1993
System of National Accounts (see Commission of the European Communities [1993]), with
a few exceptions. To make sure that the five different categories of tax revenues I use have
homogeneous elasticities, I have reclassified some of the original items. In particular, I
have reclassified in the residual item some components of income taxes or indirect taxes
that are likely to be inelastic to output at a quarterly frequency, like property taxes, fines
and penalties, inheritance taxes, etc. I have also lumped with indirect taxes items like
licenses and fees purchased by households and businesses, on the ground that they, like
indirect taxes, are probably close to being unit elastic to GDP. Under the 1993 System
of National Accounts, payroll taxes are considered as a tax on production and therefore
classified as indirect taxes; whenever the information is available, I have reclassified them
as social security taxes.