Bibliometric Indicators

Quantitative evaluation of scientific publications using statistical methods

There is no “super indicator” that would answer the question about the quality of scientific work ultimately. The question about the quality of research results is not answered, but replaced by information that makes different aspects of scientific activity and the “success” of this activity visible.

Stefan Hornbostel, Wissenschaftsindikatoren : Bewertungen in der Wissenschaft. Opladen 1997

Number of Publications (P)

The number of publications (P) provides information in absolute numbers about the productivity of an individual, a scientific group, an institution or a country. The publication numbers are quantitative in nature and provide hardly any information about the impact and quality of these works. Similarly, the publication numbers of scientists depend strongly on the displicine in which the scientist works, as well as on the size of an institution or the working years of a scientist.

Number of Citations (C)

The number of citations (C) reflects the absolute number of citations of an analyzed unit in relation to the analyzed publications within a period of time. By referring to or citing, the citing author usually attributes a certain significance to a work. The number of citations is related directly to the number of publications, it also depends on the size of the scientific institutions and the working years of a scientist. The number of citations forms the basis for calculating the citation rate.

Citation Rate (CPP)

In order to obtain information on how often an article of an analyzed unit has been cited on average, the citation rate (CPP) is calculated. Unlike the number of citations, this value is independent of the size of a research unit. Like any average value, this indicator is highly susceptible to outliers. The average annual citation rate is very dependent on publication years. If an author is scientifically active for a long time, for example, their average annual citation rate will be lower than that of someone who is scientifically active for a short time only if both authors have the same number of citations.

Hirsch Index (h-index)

In 2005, Jorge E. Hirsch proposed the index named after him to determine the value of a researcher’s scientific work. The advantages of the h-index are its simple calculation and the combination of two bibliometric measures, one being the number of publications and the other the citation rate, in one figure. Furthermore, the index is considered to be a “robust” factor, that means the factor is insensitive to extreme upward or downward outliers in publication activity. The downside of the h-index is that it is highly dependent on the scientist’s seniority in the work, meaning that the h-index increases proportionally to the length of professional activity.

For calculation, the current number of publications is sorted in ascending order and the number of the citations received in descending order. The h-index is located where the current number of publications meets the citation frequency of publications.


Time-dependent Hirsch Index

By disregarding the age of an article in the calculation of the h-index, experienced scientists who are currently making a high contribution in the scientific community cannot be compared to young scientists who are expected to have a high number of significant articles in the near future, but who currently have a low number of important articles. In order to be able to do so, the time-dependent h-index has been developed. With it, “older” articles gradually lose their “value” even if they still receive citations. With the time-independent h-index, mainly „younger“ articles are taken into account in the calculation.

Co-authorship Indicator

The co-authorship indicator expresses the share of publications that are co-authored. Various studies have shown that the number of co-authored publications is increasing continuously and that it is becoming less common for publications to be published by only one author. It has to be taken into account that authors who publish co-authored publications have better possibilities to obtain different information. Due to a high number of co-authors, an active cooperation between the authors can be observed which improves the exchange of information and therefore the exchange of opinions. Several variants have been developed for the counting of co-authors.

Share of Publications Not Cited ([%Pnc])

This indicator marks the share of publications that are not cited. There are several explanations for publications not being cited. Those could be, for example:

  • instead of original works by unknown authors, „review articles“ by known authors are cited,
  • the documents are not accessible,
  • the number of footnotes is limited artificially in order not to exceed the length of the publication,
  • citations are intentionally omitted, e.g. for competitive reasons,
  • the topic of the publication is ahead of its time.

Journal Impact Factor (JIF)

The Journal Impact Factor identifies the frequency with which an average article from a journal has been cited in a particular year. This figure can be used to evaluate the relative importance of a journal compared to others in the same field. One of the strengths of the impact factor is that it is easy to understand or quickly available. For example, it is recorded centrally and online in the Journal Citations Reports. In order to promote their journals, publishers list the Journal Impact Factor on their websites.

Classification of the Database SCImagoJR

The freely accessible database SCImagoJR lists the SCImago Journal Rank which is comparable to the Journal Impact Factor, but whose calculation includes, among other things, a journal’s prestige. The data basis for it is the database SCOPUS. A period of 3 years is used for evaluating the citations.




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