Metrics definitions
Different metrics are calculated using data from different citation and indexing databases. In addition, the types of articles counted in the calculation varies.
Impact Factor
The average number of citations in a given year per paper published in the journal over the previous two years. For example, the 2016 Impact Factor, published in 2017, is based on citations in 2016 to papers published during 2014 and 2015. Different subject areas exhibit different ranges of Impact Factor. Journals are best viewed in the context of their specific field. From Clarivate Analytics Web of Science database.
Five-year Impact Factor
Similar to the Impact Factor, but offers a smoother variation and might be more appropriate in a field where the number of citations is small or where it takes longer than two years to disseminate and respond to published works. For example, the 2016 five-year Impact Factor, published in 2017, is based on citations in 2016 to papers published during 2011 to 2015. From Clarivate Analytics Web of Science database.
Two-year citation median
The median number of citations that articles published in 2014 and 2015 received in 2016. The median is not subject to distortion by outliers. From Clarivate Analytics Web of Science database.
Eigenfactor score
A measure of the journal’s influence within the network of academic citations with a five-year target window. The score considers the origins of the incoming journal citations to articles in that journal; citations from highly ranked journals are weighted to make a larger contribution to the Eigenfactor score. Scores are not influenced by journal self-citation. From Clarivate Analytics Web of Science database.
Article Influence Score
As for the Eigenfactor score, the Article Influence Score measures influence, but on an average per-article basis. It determines the average influence of a journal's articles during the first five years after publication. The mean score is 1.00. A score greater than 1.00 indicates that the articles in a journal have an above average influence. From Clarivate Analytics Web of Science database.
Cited half-life
A measure of how long content is referred to after publication. The number of years, going back from the current year, that account for half the total citations received by the journal in the current year. From Clarivate Analytics Web of Science database.
Immediacy index
The average number of times that an article is cited in the same year it is published. From Clarivate Analytics Web of Science database.
h index
Intended to measure both the quality and quantity of scientific output, the h index is the number of articles in the journal (h) that have received at least (h) citations over the year. The measure discounts the disproportionate weight of highly cited papers or papers that have not yet been cited. The h-index only ever increases, never decreases and older articles do better than younger articles. From Elsevier Scopus database.
Scopus CiteScore
The average number of citations in a given year per paper published in the journal over the previous three years. From Elsevier Scopus database.
SJR (SCImago Journal Rank) indicator
As for the Eigenfactor score, ranks journals by their 'average prestige per article'. From Elsevier Scopus database.
SNIP (Source Normalized Impact per Paper)
Journal’s citation count per paper normalised according to its citation potential in the journal’s field. The impact of a single citation will have a higher value in subject areas where citations are less likely, and vice versa. From Elsevier Scopus database.
