On the Measurement of Horizontal Inequity


Peter J. Lambert

Publication Date:

December 1, 1995

Disclaimer: This Working Paper should not be reported as representing the views of the IMF.The views expressed in this Working Paper are those of the author(s) and do not necessarily represent those of the IMF or IMF policy. Working Papers describe research in progress by the author(s) and are published to elicit comments and to further debate


This paper makes a new attack on the old problem of measuring horizontal inequity in the income tax. Local measures of inequality of posttax income among pretax equals are proposed, which reflect alternative value judgments about the nature and magnitude of an inequity. These measures are aggregated into global indices. The welfare gain from eliminating horizontal inequity revenue-neutrally, and the revenue gain from eliminating it welfare-neutrally, in each case preserving the vertical performance of the tax, are captured by these indices. Difficulties of implementation arising from the “identification problem” are discussed. A variation in the methodology validates banding the income data to create “close equals” groups. Simulations show that the banding procedure works well. A range of potentially fruitful applications is discussed.


Working Paper No. 1995/135



Publication Date:

December 1, 1995



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