There are a variety of metrics that attempt to measure the individual journal performance. Journal metrics, such as the Journal Impact Factor by Clarivate Analytics, allow for ranking within a discipline. Authors may also use journal metrics to identify journals in which to publish. Two of the main sources for journal metrics are the Journal Citation Reports (Clarivate Analytics) and CiteScore (Scopus).
Some caveats about journal metrics:
- Metrics may be easily skewed due factors such as the proportion of review articles a journal publishes (review articles tend to have a higher citation rate) and lack of data about potentially highly cited letters and editorials, and variables in citation practices across disciplines.
- The Journal Impact Factor was developed as a decision-aid to be used by the publishers of the Institute of Scientific Investigation (now part of Clarivate Analytics) to determine which journals to index and to help librarians with journal subscription purchase choices. It was not meant to be an indicator of research impact.
- Metrics should not be used as an indicator of an individual article or author’s influence.
Selection of Indicators Included in the Journal Citation Report
Journal Impact Factor
The Journal Impact Factor is defined as all citations to the journal in the current JCR year to items published in the previous two years, divided by the total number of scholarly items (these comprise articles, reviews, and proceedings papers) published in the journal in the previous two years. Though not a strict mathematical average, the Journal Impact Factor provides a functional approximation of the mean citation rate per citable item.
The Immediacy Index is the average number of times an article is cited in the year it is published. The Immediacy Index is calculated by dividing the number of times an article is cited in the year it is published.
Because it is a per-article average, the Immediacy Index tends to discount the advantage of large journals over small ones. However, frequently issued journals may have an advantage because an article published early in the year has a better chance of being cited than one published later in the year. Many publications that publish infrequently or late in the year have low Immediacy Indexes.
Average JIF Percentile
The Average Journal Impact Factor Percentile is based on the Journal Impact Factor Percentile (JIF Percentile). The JIF Percentile simply translates a journal’s category rank into a percentile. For example, a journal that is ranked 19 out of 291 Biochemistry & Molecular Biology journals would receive a JIF Percentile score of 94. JIF Percentiles are scaled from 1 to 100 (higher values indicate higher Impact Factor in relation to other journals in the Category). The metric allows you to assess the journal’s standing in its own subject field.
By factoring in a journal’s impact factor within its specific subject field, as well as controlling for the size of the field, the JIF Percentile is normalized and so allows comparison between journals in different subject areas. For example, assessing the impact of a medical journal against an engineering journal in a deeper way than simply comparing their respective Journal Impact Factors.
The Eigenfactor Score attempts to provide a metric that measures the total influence of a scientific journal. Journals are rated according to the number of incoming citations, with citations from highly cited journals weighted to make a larger contribution to the Eigenfactor. The Eigenfactor score is intended to measure the importance of a journal to the scientific community, by considering the origin of the incoming citations, and is thought to reflect how frequently an average researcher will be redirected back to a journal by following the citations in the articles they find interesting. Typically, journals with a higher JIF have corresponding larger Eigenfactor scores. See the Eigenfactor Project for more information.
Journal Metrics Found in Scopus
The CiteScore is based on the average citations received per document. CiteScore is the number of citations received by a journal in one year to documents published in the three previous years, divided by the number of documents indexed in Scopus published in those same three years. CiteScore’s numerator and denominator both include all document types. This not only includes articles and reviews but also letters, notes, editorials, conference papers and other types indexed by Scopus. Therefore, the numerator and the denominator used in the CiteScore calculation are consistent. This approach gives a more complete picture of citation impact and makes manipulation of the calculation more difficult. Articles-in-press are indexed in Scopus for some publishers, but are not included in the CiteScore calculation.
Scimago Journal Rank (SJR)
This metric is a field-normalized metric that is an alternative to the Journal Impact Factor. It uses Scopus citation data to calculate the weighted prestige of a journal based on the number of citations received by a journal and the prestige of the journals where the citations originate. With SJR, the subject field, quality and reputation of the journal has a direct effect on the value of a citation. Its method of calculation attempts to normalize for differences in citation behavior between subject fields.
Source Normalized Impact per Paper(SNIP)
SNIP is a field-normalized metric that measures a source’s contextual citation impact by weighting citations based on the total number of citations in a subject field. It helps you make a direct comparison of sources in different subject fields.
SNIP takes into account characteristics of the source’s subject field, which is the set of documents citing that source. SNIP especially considers:
- The frequency at which authors cite other papers in their reference lists
- The speed at which citation impact matures
- The extent to which the database used in the assessment covers the field’s literature
SNIP is the ratio of a source’s average citation count per paper and the citation potential of its subject field.
The citation potential of a source’s subject field is the average number of references per document citing that source. It represents the likelihood of being cited for documents in a particular field. A source in a field with a high citation potential tends to have a high impact per paper.
Citation potential is important because it accounts for the fact that typical citation counts vary widely between research disciplines. For example, they tend to be higher in life sciences than in mathematics or social sciences. If papers in one subject field contain an average of 40 cited references while those in another contain an average of 10, then the former field has a citation potential that is 4 times higher than that of the latter.
Citation potential also varies between subject fields within a discipline. For instance, basic journals tend to show higher citation potentials than applied or clinical journals, and journals covering emerging topics tend to have higher citation potentials than periodicals in well-established areas
The CiteScore Perentile indicates the relative standing of a journal in its subject field. A CiteScore Percentile of 98% means the journal is in the top 2% of its subject field. You can use this number to compare journals in different subject fields. CiteScore Rank and Rank Out Of
The CiteScore Rank and Rank Out Of indicates the absolute standing of a serial in its field; for example, 14th out of 63 journals in the category.