World Income Inequality Database
The World Income Inequality Database (WIID) contains information on income inequality in various countries, and is maintained by the United Nations University-World Institute for Development Economics Research (UNU-WIDER). The database was originally compiled during 1997-99 for the research project Rising Income Inequality and Poverty Reduction, directed by Giovanni Andrea Corina. A revised and updated version of the database was published in June 2005 as part of the project Global Trends in Inequality and Poverty, directed by Tony Shorrocks and Guang Hua Wan. The database was revised in 2007 and a new version was launched in May 2008.
World Income Inequality Database (WIID) v. 2.0a
Data types and sources
Income data based on surveys, official records and national accounts. The data are collected from several primary and secondary sources, such as Klaus Deininger and Lyn Squire’s Measuring Income Inequality Database (see Deininger and Squire 1996), the Luxembourg Income Study (LIS), the Transmonee data by UNICEF/ICDC, national statistical offices and other research studies.
The database contains data on inequality in the distribution of income in various countries. The central variable in the dataset is the Gini index, a measure of income distribution in a society. In addition, the dataset contains information on income shares by quintile or decile.
The database contains data for 159 countries, including some historical entities.
Time coverage and updates
The temporal coverage varies substantially across countries. For some countries there is only one data entry; in other cases there are over 100 data points. The earliest entry is from 1867 (United Kingdom), the latest from 2006. The majority of the data (65%) cover the years from 1980 onwards. The 2008 update (version WIID2c) includes some major updates and quality improvements, in fact leading to a reduced number of variables in the new version. A summary of the latest version can be found here.
Access conditions and cost
Available free of charge.
Comparability and data quality
The database has been compiled to allow for comparisons of income inequality across time and space, but several factors may nonetheless affect the comparability of the data. The data are collected from a variety of sources, frequently using different definitions and methods of data collection. Users must therefore examine the documentation carefully before using the data. See Atkinson and Brandolini (2001), Deininger and Squire (1996) and UNU-WIDER (2005) for discussions of the quality and comparability of income distribution statistics.
Atkinson, Anthony B., and Andrea Brandolini. 2001. “Promise and pitfalls in the use of ‘secondary’ data-sets: income inequality in OECD countries as a case study”. Journal of Economic Literature 39 (September): 771-799.
Deininger, Klaus, and Lyn Squire. 1996. “A new data set measuring income inequality”. World Bank Economic Review 10 (3): 565-591.