Web of Science indicators
Web of Science is a bibliographic citation database that uses measures scientific publications through the Impact Factor. This is a main tool for the analysis of citation frequency and patterns in scientific production. First known (since 1963) as the Science Citation Index of the ISI (Institute for Scientific Information), that has now become Web of Science (WOS). WOS is a bibliographic database that grants a very broad coverage both temporally and in terms of scientific output.
Indicators used by WOS at an article level
Citation Index ("Times cited")
An article-level metric based on the count of citations received by an article published in journals indexed in the Web of Science Core Collection. This is a bibliographic database accessible online through institutional authentication or university network. The calculation is performed over a very wide time span: from 1900 for journals in the Science Citation Index (SCI) or the Social Sciences Citation Index (SSCI), and from 1975 for those in the Arts & Humanities Citation Index.
“Times cited” is an index of citations for each article ad it appears alongside the bibliographic reference as the number of citations received.
Moreover, alongside the reference Usage Count, another metric (non-citation based), can be found. This measures the interest in the article through the link to the full-text or through saving the citation for use in bibliographic management software
Indicators used by WOS at a journal level
This is the most well-known bibliometric index, introduced in 1975 within the Journal Citation Reports (JCR).
It is covered by copyright and is available through the university network.
The Impact Factor measures the number of citations received by articles published in a scientific journal in the two preceding years. It indicates how important a scientific journal is based on the impact of the the “average” article over a relatively short period. This way the journals can be ranked for each disciplinary field considered by the Journal Citation Report.
Its value varies depending on the disciplinary areas because each community is characterized by specific citation behavior, so it is necessary to take into account the average trend of the IF in that area of relevance (normalized IF).
The Journal Citation Reports, using the Impact Factor, annually ranks journals in their disciplinary sector. Journals do not always belong to a single discipline and may appear in more than one ranking.
The normalization of the IF and the subdivision into quartiles is necessary to try to solve the problem of the heterogeneity of the weight of the IF in various disciplines. The positioning of the journal within the quartile will depend on the positioning of its IF in the distribution of Impact Factors in a specific disciplinary field.
Q1: positions within the first 25% of the normal curve representing the IF distribution (journals with high IF)
Q2: positions between 25 and 50%
Q3: positions between 50-75%
Q4: positions above 75%
Usually, since a journal may appear in more than just one disciplinary sector, the journal is associated with a quartile score coming from a uniform distribution of its quartile placements.
Criticism
Purely quantitative: counting citations regardless of their value and content. The IF rankings are compiled for various disciplinary categories, wrongly assuming that a high citation frequency corresponds to a high scientific value of the journal.
Only a sample of selected journals: IF data are available only for some selected journals indexed in the Journal Citation reports (JCR).
The IF can be influenced by factors unrelated to content quality.
Deriving from IF
Immediacy index
It estimates the speed at which an article is cited on average, measuring how successful a work is in a year, indicating the degree of innovation, originality, and newness of the published content. It is calculated dividing the number of citations the journal receives in a year by the number of articles published in the same year.
Cited half life
It measures the worth of articles over time by analyzing the distribution over time of citations in journals. It is calculated by adding the number of publication years, starting from the current one and going back in time, in which 50% of the total citations received by that journal in the current year were recorded.
Citation Impact
It is calculated for a specific subject, author, or institution and is obtained by deviding the number of citations received by the number of articles published.
This is an open-access indicator for journals that was developed as a research project at the University of Washington.
The Eigenfactor is based on a mathematical model that takes into account the different citation standards across disciplines and uses the entire citation network structure to evaluate the importance of each journal.
The EF is based on citations over the last 5 years (not two like the IF) because in some research areas, articles do not have a high citation frequency until several years after publication.