The econophysics “two-class” approach yields a novel theoretical and empirically robust relation: The per capita income (Formula presented.) of any bottom fraction (x) of the population equals a(x)∙(1−G) (Formula presented.), where a(x) is a coupling coefficient, G the Gini, and (Formula presented.) is national per capita income. For the bottom 70%, a(70) = 1, which yields the Sen inequality