Linguistic diversity index (LDI) may refer to either Greenberg's (language) Diversity Index [1] or the related Index of Linguistic Diversity (ILD) from Terralingua, which measures changes in the underlying LDI over time. [2]
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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). [3] The ILD measures how the LDI has changed over time; a global ILD of 0.8 indicates a 20% loss of diversity since 1970, but ratios above 1 are possible, and have appeared in regional indexes. [4]
The computation of the diversity index is based on the population of each language as a proportion of the total population. The index cannot fully account for the vitality of languages. Also, the distinction between a language and a dialect is fluid and often political. A great number of languages are considered to be dialects of another language by some experts and separate languages by others. The index does not consider how different the languages are from each other, nor does it account for second language usage; it considers only the total number of distinct languages, and their relative frequency as mother tongues. [5]
