the concept of Zipf’s law, respectively. The second most cited concept of the PLE has been cited by authors of articles representing
12 topics on information behavior research, followed by bibliometrics research and information retrieval research.
Although authors of only nine articles have cited the concept of HBPLE; most of the citations were from bibliometrics researchers.
4.5. Citation functions
Table 5 shows the distribution of 11 citation functions based on 310 citation contexts. The top five citation functions
were close in percentage and ranged from 11.0% to 17.1%. “Evidence” supporting citing authors’ claims was dominant (17.1%),
followed by “comparison” (16.8%), which referred to comparing the findings or claims of HBPLE and results of other studies.
“Related studies” referred to the basic part of a scientific paper presenting the findings of previous studies. “History” referred
to the tracing of pioneers or earlier works with the aim of offering background information. “Relationship” referred to the
foundation of Zipf’s claims; Zipf’s claims then became the foundation of other claims. “Definitions” referred to those of
concepts that originated from HBPLE. “Examples” referred to HBPLE or to Zipf’s claims being given as examples to clarify
the author’s ideas. “Further reading” referred to suggestions that readers read HBPLE to obtain a deep understanding of
certain concepts. Finally, “Method” referred to the provision of detailed information regarding the methodology used in
Zipf’s studies.
Table 6 shows the distribution of 17 cited concepts in 11 citation functions. The most frequently cited concept was Zipf’s
law and was mainly used for comparison with other bibliometric laws, whereas the second-most cited concept, the PLE,
was mainly used as evidence. The same concepts could have numerous citation functions. In addition, this reflected the
complications of citing publications (Bonzi & Snyder, 1991; Liu, 1993).