Applicability of Zipf's Law in Traditional Chinese Medicine Prescriptions.

Objective Traditional Chinese medicine (TCM) prescriptions have been used to cure diseases in China for thousands of years, in which many TCM herbs have no definite common quantity. Some key TCM herbs are commonly used and thus deserve in-depth investigations based on a more acceptable classification method. This study analyzes whether TCM prescriptions follow Zipf's law and attempts to obtain the thresholds of key TCM herbs based on the application of Zipf's law. Methods A total of 84,418 TCM prescriptions were collected and standardized. We tested whether Zipf's law and Zipf's distribution fit the Chinese herb distributions. A linear fitting experiment was performed to verify the relationship between the frequency distribution and frequency of TCM herbs. Results The distribution of TCM herbs in TCM prescriptions conformed to Zipf's law. Accordingly, the thresholds were obtained for the key TCM herbs. Conclusion The distribution of TCM herbs in TCM prescriptions follows Zipf's law.