Linguistic demography
（重定向自Demolinguistics）
Linguistic demography is the statistical study of languages among all populations. Estimating the number of speakers of a given language is not straightforward, and various estimates may diverge considerably. This is first of all due to the question of defining "language" vs. "dialect". Identification of varieties as a single language or as distinct languages is often based on ethnic, cultural, or political considerations rather than mutual intelligibility. The second difficulty is multilingualism, complicating the definition of "native language". Finally, in many countries, insufficient census data add to the difficulties.