(en) While there exist various descriptive measures of horizontal and vertical concentration, and an endless discussion of their respective merits, there has been, till recently, a lack of comparable reflections and proposals in the measurement of conglomerate, concentration or diversification.
Jacquemin, A. P. (1974). An Entropy Measure of Diversification (Working Papers Institut des sciences économiques 7416). https://hdl.handle.net/2078.5/275760