Levels of Bilingualism

How many people in the world speak more than one language? Probably the vast majority. In the USA it's estimated at 18% (US Census Bureau), in Canada it's about 34% (Statistics Canada) and in the EU it's about 66% (European Commission). But getting data is hard - even in countries with the infrastructure to support a large scale census, the issue of bilingualism is often not prioritised. The metric of number of languages spoken in each country (linguistic density) has been used (e.g. Nettle, 1999), as well as the number of neighbour groups (Lupyan & Dale, 2009) and is probably correlated, but is not the same as bilingualism.

So, maybe we can estimate a different way. The Ethnologue has data on the estimated number of speakers for each language within a country, along with the number of people in a country. Subtracting the number of speakers from the number of people gives, in theory, the maximum number of bilinguals in a country.

Maximum Number of Bilinguals =
total number of speakers for all languages – total number of people

For example, if a country has 1 million people, and 500,000 speakers of language A and 750,000 speakers of language B, then 250,000 must be bilingual (if there are no other languages spoken). The figure below shows the ratio of speakers to people with darker areas indicating higher levels of bilingualism (data from Ethnologue, created with R):

click for larger image

As expected, the data is not good enough to warrant a proper analysis. The number of speakers is underestimated (total population of world = 6 billion, total number of speakers = 5.7 billion). 12% of entries in the ethnologue have no population data and for more than half of the countries the number of speakers is less than the number of people. One exception was Saudi Arabia, with a ratio of 9.4, possibly because 23% of the population are foreign nationals or, more intriguingly, because the majority of the population were nomadic until the 1960s.

At any rate, there appears to be no correlation with latitude (r= -0.1, t = -1.4, df = 197, p-value = 0.15) or longitude (r = -0.01, t = -0.28, df = 198, p-value = 0.8).

Ah well, back to counting people instead of numbers.
Gary Lupyan, Rick Dale (0). Linguistic Structure is Partly Determined by Social
Structure in Press