where y j is the income share of group j in total income and p j is the population
share of group j in the total population.2 As articulated in Anand (1983), one
appealing feature of the Theil indices is that the income inequality measure can
be additively decomposed into within-group and between-group inequality components
(denoted with the subscripts W and B, respectively). Suppose that all
individuals in the population are grouped into m groups. GE(0) can be partitioned
into the two components as follows: