Piketty (2001) pointed out the strong heterogeneity of the top decile. Piketty’s methodology is applied here, and is fully described in Les hauts revenus en France au XXème siècle 15 . Piketty’s book deals with the upper income shares over the past century, and focuses on France’s individual tax returns in the 20th century. It includes voluminous appendices detailing step by step the 'why's and 'why not's of the methodology used. The methodology can be broken into two steps: 1) the definition of the fractile tables that need to be created for each state and for each year between 1913 and 2003, and 2) the interpolation method used to estimate each of them.
The Upper Shares of Income in France in the 20 th Century.