Linguistic diversity index

Linguistic diversity index (LDI) may refer to either Greenberg's (language) Diversity Index or the related Index of Linguistic Diversity (ILD) from Terralingua, which measures changes in the underlying LDI over time. Greenberg's Diversity Index (LDI) is the probability that two people selected from the population at random will have different mother tongues; it therefore ranges from 0 (everyone has the same mother tongue) to 1 (no two people have the same mother tongue).

Source: Wikipedia — Linguistic diversity index (CC BY-SA 4.0)