Statistical studies of languages have focused on the rank-frequency distribution of words. Instead, we introduce here a measure of how word ranks change in time and call this distribution \emph{rank diversity}. We calculate this diversity for books published in six European languages since 1800, and find that it follows a universal lognormal distribution. Based on the mean and standard deviation associated with the lognormal distribution, we define three different word regimes of languages: "heads" consist of words which almost do not change their rank in time, "bodies" are words of general use, while "tails" are comprised by context-specific words and vary their rank considerably in time. The heads and bodies reflect the size of language cores identified by linguists for basic communication. We propose a Gaussian random walk model which reproduces the rank variation of words in time and thus the diversity. Rank diversity of words can be understood as the result of random variations in rank, where the size of the variation depends on the rank itself. We find that the core size is similar for all languages studied.

该研究介绍了一种对时间变化中词汇排名进行测量的“排名多样性”分布，并通过对六种欧洲语言的1800年至今的书籍进行实证研究，发现其呈现出普遍的对数正态分布。研究者们提出了一种高斯随机漫步模型来解释这些单词在时间中的排名变化，这些变化可以理解为排名的随机波动，其中变化的大小取决于其本身的排名，并发现这种分布的核大小在所有研究的语言中都相似。

计算语言学中的语言排名多样性：通用行为