Fitting Ranked Linguistic Data with Two-Parameter Functions

It is well known that many ranked linguistic data can fit well with one-parameter models such as Zipf's law for ranked word frequencies. However, in cases where discrepancies from the one-parameter model occur (these will come at the two extremes of the rank), it is natural to use one more parameter in the fitting model. In this paper, we compare several two-parameter models, including Beta function, Yule function, Weibull function-all can be framed as a multiple regression in the logarithmic scale-in their fitting performance of several ranked linguistic data, such as letter frequencies, word-spacings, and word frequencies. We observed that Beta function fits the ranked letter frequency the best, Yule function fits the ranked word-spacing distribution the best, and Altmann, Beta, Yule functions all slightly outperform the Zipf's power-law function in word ranked-frequency distribution.