Decomposition of income inequality by groups formed of individuals
possessing similar characteristics (e.g., sex, education, age) and their
income sources at the same time.
Decomposition of the Theil index is based on Giammatteo, M. (2007)
< https://www.lisdatacenter.org/wps/liswps/466.pdf>.
Decomposition of the squared coefficient of variation is based on
Garcia-Penalosa, C., & Orgiazzi, E. (2013)
Two-dimensional decomposition of the Theil index and squared coefficient of variation.