Journal impact measures the influence or importance of a particular journal in a discipline. Journal impact metrics take into account the number of articles published per time period and the number of citations to articles published in that journal. They can help track citation patterns within journals and determine which journals are highly cited.
There are many factors that influence the impact of a journal and each tool may produce varying results depending on the scope of its database. For a more accurate picture of journal impact, you can use more than one tool to compare results.
SCImago Journal Rank (SJR)
“The SCImago Journal Rank is a portal that includes the journals and country scientific indicators developed from the information contained in the Scopus® database (Elsevier B.V.).” Scopus contains more than 15,000 journals from over 4,000 international publishers as well as over 1000 open access journals. The SJR measures citations weighted by prestige. It is useful for comparing journals within the same field, and forms the basis of the subject category ranking. Q1 journals are cited more often and by more prestigious journals than those in the other quartiles.
SNIP (Source Normalized Impact per Paper)
The SNIP (Source Normalized Impact per Paper) measures citations weighted by the subject field. It is useful for comparing journals not just within the same field but also across disciplines. A SNIP of 1.0 means that a journal’s articles are cited at the average rate for all journals in the same subject area; anything over 1.0 indicates more citations than average in the field while a SNIP of less than 1.0 is below the average. A SNIP of more than 1.5 generally indicates a very well-cited journal.
CWTS Journal Indicators offers a number of bibliometric indicators on scientific journals. These indicators have been calculated based on the Scopus bibliographic database produced by Elsevier.
CiteScore is a metric for measuring journal impact in Scopus and is based on the average citations received per document. CiteScore calculates the number of citations received by a journal in one year to documents published in the three previous years, divided by the number or documents indexed in Scopus published in those same three years. The CiteScore is useful for comparing journals within the same field, ranking them in subject categories and indicating the percentile they fall into.
Eigenfactor scores are intended to give a measure of how likely a journal is to be used and how frequently an average researcher would access content from that journal.