The Standardized Income Distribution Database (SIDD) is based on a comprehensive collection of income distribution data compiled by the United Nations University's World Institute for Development Economics Research, the World Income Inequality Database (WIID), Version 1. The SIDD adjusts the raw WIID data for differences in scope of coverage, income definition, and reference unit to a nationally representative, gross income, household per capita standard. The SIDD is also clean, free of duplicates, and easy to access. Peer-reviewed documentation of the SIDD have been published in:

• SIDD-1: Babones, Salvatore J., and Maria Jose Alvarez-Rivadulla. 2007. "Standardized Income Inequality Data for Use in Cross-National Research." Sociological Inquiry 77(1): 3-22.

• SIDD-3: Babones, Salvatore J. 2008. "Standardized Income Inequality Data for Use in Cross-National Research." Sociological Inquiry 77:3-22.

• SIDD-1: Each data point in the SIDD-1 has been adjusted for its scope of coverage (nationally representative, urban population, or working population), its income definition (gross income, net income, or consumption), and its reference unit (household per capita, household per capita adjusted, or social assistance unit). The SIDD-1 can be thought of as a cleaned and standardized version of the WIID data. The SIDD-1 graphical tool allows users to create fitted time series plots of SIDD-1 data.
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• SIDD-2: The SIDD-2 is similar to the SIDD-1, except that all adjustment factors have been estimated separately for developed and developing countries. The SIDD-2 graphical tool allows users to create fitted time series plots of SIDD-2 data.
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• SIDD-3: The SIDD-3 is an interpolated and extrapolated version of the SIDD-2 incorporating in-sample and out-of-sample estimates for the full period 1955-2005.
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