The maths of arresting decline of Gaelic

I know the Barnett Formula is a real mathematical equation, but I'm staggered to come across this model which measures the shift from Gaelic speaking across to English bilingualism.



The formula, which explains how we all end up speaking English, comes from the Royal Society paper on bilingualism and the future of the Celtic languages.

The intriuging maths apart, the important caclulation in the paper is that to 860 people would have to become bilingual in Gaelic each year if the decline of the language was to be halted. That's a tall order despite the phenomenal level of interest and determination of Gaelic learners.

But it's not all up to learners to save the language. Here's the crucial passage for the remaining 65,000 Gaelic speakers:

"Intervention strategies may prove much more successful if the rate of intergenerational transmission of the bilingual strategy could be increased as well. Thus, for example, the number of English monolinguals required to learn Gaelic each year could drop down to roughly 440 if the rate of intergenerational transmission of Gaelic at home could be increased (c12 from 0.025 to 0.0125).

This means that beside the 440 new recruits to bilingualism, roughly 340 more children who live in bilingual households would have to be raised in both languages to stabilize the bilingual population at the current level. These numbers indicate that an increase in the rate of intergenerational transmission is a highly effective language maintenance strategy, although one that is also harder to achieve in practice."