Bilingualism Delays Onset of Dementia

Dee writes with word of a Canadian study indicating that lifelong bilingualism delays the onset of dementia by 4 years. The scientists were reportedly "dazzled" by the results. From the article: "The researchers determined that the mean age of onset of dementia symptoms in the monolingual group was 71.4 years, while the bilingual group was 75.5 years. This difference remained even after considering the possible effect of cultural differences, immigration, formal education, employment and even gender as influencers in the results. "

Comments

Re:statistics

[dorpus]

Normally, we would test a difference in means between two populations by a t-test. If the sample size is large enough, then even a difference that is only a fraction of a standard deviation can be statistically significant. F-tests are used in ANOVA tables, and yes, they do assume normal distributions, as well as homoskedasticity (same variance). Assuming they performed a linear regression, then one can perform a Type I F-test (added-in-order test) or Type II F-test (added-last test). One can also talk about an overall F-test, testing whether any of the effects in the model are nonzero. However, as I indicated in another post, the study only had 184 patients from a single treatment center. There is selection bias, since the study only sampled patients who were already suffering from memory loss. How many other bilingual immigrants with memory loss are lurking in the general population, who aren't going to memory loss clinics due to lack of knowledge? Also, what method did they use to adjust for "cultural differences, immigration, formal education, employment and even gender" with only 184 patients? The study only proves that bilingual patients who arrived at a particular treatment center were, on average, 4 years older than monolingual patients. It does NOT provide a causal link between bilingualism and cognitive reserve.

Re:I do a wee bit better than that.

[christophe]

in Western Europe it is de rigueur to speak at least three languages. Well, Western Europe is a big place with many different nations. You can expect people from small countries, like Swiss or Belgians, to be fluent in one or two foreign languages, and people from Sweden or Danemark to speak very good English and often German. But the average French barely speaks enough English for international business (with many exceptions), and English people don't even have to learn another language. Situation seems better in Germany, at least for English. IMHO, that has more to do with the educational system and motivation than anything else. Exposure to foreign content (most films in original version with subtitles on TV for example, as in Danemark) is another key.

(Spoken as a French which speaks three languages).