The Hirsch index (H-index) is a tool to evaluate the scientific performance of authors.
The H-index of an author is N when at least N papers have been cited N times. A H-index can only increase, even though an author has become inactive. The H-index of a young excellent scientist will always be small, H-indexen are determined using databases such as Web of Science, Scopus of Google Scholar. This will result in different values. Selfcitation can be excluded from the calculations. Differences between disciplines affect values of a H-index.
Scientific papers are connected by citing and referencing. Following these connections might result in finding interesting new papers. The ISI Citation Indexes, now known as Web of Science, have been developed to study who cited a specific paper. Platforms such as Scopus, or the publishers now also offer this function, usually called “cited by” or “number of citations”.
Citation analysis has been evolved into a tool to evaluate scientific performance. The basic assumption is that a more important paper has been cited more often. This assumption ignores differences between disciplines in the number of papers an author produces, the number of co-authors, the number of references. Normalization of data offers the opportunity to compare disciplines.
Recent papers are undervalued in citation analyses.
The Impact factor of journals is determined with data from Web of Science. The Impact factor equals the average number of citations to papers in a journal, during the last 2 years. Impact factors are dependent on scientific discipline. Therefor organisations like CWTS try to normalise data. An overview of Impact factors can be found in the Journal Citation Reports.
The SCImago Journal Rank also takes into account the prestige of the citing journal. This mechanism is similar to Pagerank, the mechanism used by Google to sort the results.SJR’s can be found in Scopus Analytics