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The number of citations received in publications is calculated by citation databases, e.g. citation indexes which, starting from a specific scientific article, enable you to retrieve and count all citations received in the bibliographies of the articles published in a selected group of international academic journals.

 Again through these evaluation tools based on the analysis of citations, the bibliometric indicators most used to evaluate the impact of journals and authors are constructed: Impact Factor (IF) and H-Index.

 The following are the main evaluation tools based on citation analysis:

 

 Web of science <http://apps.webofknowledge.com> (paid database; reserved access for UniPa users)

 Produced by the Institute of Scientific Information (ISI) and traditionally published by Thomson Reuters, the WoS database (recently taken over by Clarivate Analytics) is a multidisciplinary service which, by accessing data from different electronic archives, indexes metadata and contents of thousands of scientific journals selected on the basis of their compliance with specific attributes, ensuring their integrity and authority in the relevant disciplinary field: impact, influence, punctuality, peer review, international distribution.

In addition, The WoS service provides information about the citations received in published articles, also in the form of citation indices of the authors’ contributions, i.e. to know how many times the work of an author has been cited (citation index), and to calculate the H-Index of each author, who is uniquely identified in the database through a specific disambiguation code (Researcher ID).

WoS includes specific sections/databases: Science Citation Index (SCI), Social Sciences Citation Index (SSCI), Arts and Humanities Citation Index (AHCI). There is another database, of a multidisciplinary nature, distinct and separate from the previous ones, called Emerging Sources Citation Index (ESCI), containing the journals whose publication meets the valid criteria for the selection procedure of journals in WoS (namely: being peer reviewed, following good practices and a code of ethical conduct for publication, complying with some technical requirements, having bibliographic information in English, being recommended by academics who use Web of Science), but which have not yet been included in the Core Collection

 

The Journal citation reports (JCR) <https://clarivate.com/products/journal-citation-reports/> (paid database, derived from WoS; reserved access for UniPa users) are a fundamental tool for evaluation and comparison of scientific journals around the world, based on the analysis of citations. JCR are available in two editions: Science edition, containing data from thousands of journals in the field of STM (scientific technical and medical disciplines) and Social sciences edition, containing data from thousands of journals in the SSH (social sciences and humanities). JCR allow to elaborate various impact measures, including: Impact factor - Immediacy index - Cited Half life.

 

 Scopus <http://www.scopus.com/home.url> (paid database; reserved access for Unipa users)

 Produced and published by Elsevier, Scopus is a bibliographic database providing wide international coverage which has been used for several years as a reference source for the calculation of citations in addition to or as an alternative to the Web of Science indexes. Like WoS, Scopus is a paid citation database enabling to carry out the citation analysis of the authors' scientific production, and to calculate the H-Index of a single author, uniquely identified in the database through a specific disambiguation code (Scopus ID).

 

Google Scholar <http://scholar.google.com/> (open access search engine)

Google Scholar is the tool created by Google for researching academic publications on the net. In the same way as the well-known word engine, it indexes scientific literature since the ‘70s, searches and retrieves a large variety of scientific documents online (articles by academic publishing houses, essays, peer-reviewed publications, theses, books, preprints, abstracts and technical reports, databases of unpublished studies, universities and other academic organizations). The available materials refer to all areas of knowledge and come from scientific publishers, universities, preprint archives; Google Scholar enables citation search and provides access to full-text, where available.

Recently, Google has also developed a product proposing itself as a source for counting citations, alternative to Web of Science and Scopus; unlike these two databases, Google scholar is open access. It allows to carry out the citation analysis of the authors and their publications and to calculate the H-Index with the aid of specific free tools capable of querying the bibliographic archives present on Google Scholar and processing the information (Publish or Perish, QuadSearch - MetaSearch Engine, scHolar INDEX to name a few). However, it should be noted that Google Scholar does not yet have a level of data reliability and refinement enabling it to compete with other citation indices for official research quality assessment purposes, therefore national rating agencies do not currently take it into consideration for these purposes.