Theil

Theil is a surname of Dutch origin that appears in the Netherlands and in other countries. The name is best known in statistics and economics through Henri Theil, a Dutch econometrician whose work led to the development of entropy-based measures of inequality and to contributions in econometric theory. The term Theil is widely encountered in the form of the Theil index, a statistic used to quantify the dispersion or concentration of a variable such as income or consumption.

The Theil index is part of the generalized entropy family of inequality measures and has two common variants, Theil T and Theil L. It draws on concepts from information theory and can be interpreted as an average log deviation of individual shares from the mean. A defining property is decomposability: total inequality can be split into within-group and between-group components when the population is divided into subgroups, enabling analysis of how different groups contribute to overall inequality. The Theil index is used across economics, statistics, and related disciplines to study distributional patterns and policy impacts.

Theil also appears in geography as part of French place names. In France, several communes or localities include the toponym Le Theil (and related forms), reflecting historical linguistic and regional naming practices. These uses are independent of the statistical concept but share the same linguistic root.

See also: Theil index, Henri Theil, toponymy.