Index of Linguistic Diversity

Calculating trends in species and languages

One way that biologists assess the state of biodiversity is to use indices based on average trends in the populations of a selection of species, such as the WWF/ZSL Living Planet Index (LPI), published since 1998. The LPI is based on time-series data for approximately 9,000 vertebrate species populations (of about 2,600 different species) from around the world.

In 2010 we adapted the LPI method to create the Index of Linguistic Diversity (ILD). The ILD uses trends in the numbers of speakers across a random, representative sample of 1,500 languages to calculate average trends. Data on numbers of mother tongue speakers (MTS) for each language going back to 1900 were extracted from editions of Ethnologue, the standard source for basic information about the world’s 7,000+ languages. The ILD calculates the average trend in MTS of those languages
in the sample. The ILD is a measure of trends in linguistic
diversity for all languages in the world, and may be compared with the global LPI to see relative trends in linguistic diversity and biodiversity. To facilitate regional comparisons between the two indices, we also calculated the ILD by biogeographic realm. The ILD Global trendline is shown top right; at the bottom of this page, a world map with regional ILDs overlaid on it.

What does the ILD measure?

The ILD measures trends in the fraction of the total population belonging to each language. To use an economic analogy, it is like an index of average market
share of languages. If the average market share declines, it means that a few languages are increasing their market share at the expense of a greater number of others; that is, more of and more of the world’s people are speaking fewer and fewer languages. As the upper-right graph shows, this is exactly what has been happening since 1970, the starting point of the index. Since then, the world’s linguistic diversity has declined by about 20% (almost exactly the same as the decline in the LPI (dark green line in the graph) over the same period).

How is the ILD being used?

Most prominently, the ILD has been selected as the indicator of progress toward the Convention on Biological Diversity’s Aichi Target 18 on the preservation of traditional knowledge.


What’s next? ILD 2020

The ILD was last revised in 2014. We now are planning an entirely new edition, called ILD 2020, that will include every language in the world—over 7,000 in all—instead of a sample subset. We will expand our methodology and analyses to allow us to calculate ILDs by major language family, and by country, in addition to the existing global and regional ILDs. We will develop new data visualizations to help people grasp the meaning of trends in linguistic diversity. These might include such things as interactive maps, innovative charting methods, and linked audio and video clips of actual speakers of the languages. We are currently seeking funding for ILD 2020.

Learn more about the ILD

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