He showed that the tenth most frequent word occurred 2,653 times, the hundredth most frequent word occurred 265 times, the two hundredth word occurred 133 times, and so on. Zipf's Law, again, is not statistically perfect, but it is very useful for indexers. Another major area of bibliometric research uses various methods of citation analysis in order to establish relationships between authors or their work. Here is a definition of citation analysis, and definitions of co-citation coupling and bibliographic coupling, which are specific kinds of citation analysis. When one author cites another author, a relationship is established.
Citation analysis uses citations in scholarly works to establish links.
Many different links can be ascertained, such as links between authors, between scholarly works, between journals, between fields, or even between countries. Citations both from and to a certain document may be studied. One very common use of citation analysis is to determine the impact of a single author on a given field by counting the number of times the author has been cited by others. If papers A and B are both cited by paper C, they may be said to be related to one another, even though they don't directly cite each other. If papers A and B are both cited by many other papers, they have a stronger relationship.