6. Conclusion
HBPLE is a classic work on linguistics that has been cited by authors representing various disciplines, including LIS. This
study tracked the influence of HBPLE on LIS research. An increasing trend in the annual number of citations indicated that
the influence of HBPLE on LIS research has not yet diminished. Based on the findings, the influential concepts embedded in
HBPLE and which topics in LIS research have been affected by HBPLE were identified. In particular, I focused on the visibility
of the concept of the PLE, which comprises the core of HBPLE. Citation context analysis helped to clarify the relationship
in terms of content between HBPLE and LIS research and to explore the citation functions of HBPLE. The most substantial
discovery was the fact that the concept of Zipf’s law has greater visibility than does the concept of the PLE. A concept
highlighted in a publication may not receive substantial attention. This implies that citing behavior is complicated and that
various motivations for citing publications also affect the visibility of cited publications. In addition, I observed that the
influence of HBPLE is visible in numerous areas in LIS research. Information behavior researchers exhibited the most interest
in the concept of the PLE whereas bibliometrics researchers paid the most attention to the concept of Zipf’s law. Although
a close relationship exists between the PLE and Zipf’s law, they exert an evidently different influence. Because HBPLE has
had an interdisciplinary influence and because citing behavior varies among disciplines, I suggest that future studies aim to
identify the influence of HBPLE on various disciplines. Based on the WoS data, I determined that although HBPLE is a classic
work on linguistics, it substantially influences numerous fields outside linguistics.