Journal metrics measure, compare, and often rank research and scholarly publications. They can also be referred to as journal rankings, journal importance, or a journal's impact. Journal metrics allow scholars and researchers to compare scholarly periodicals.
The original citation impact metric is the Journal Impact Factor, created in the 1950s, and available through Thompson Reuters' Journal Citation Reports. More recently, a variety of other free journal metrics have been created, including CiteScore, Eigenfactor, Google Scholar Metrics, SCImago Journal & Country Rank (SJR), and Source Normalized Impact per Paper (SNIP).
Each journal ranking metric uses its own formula to determine a journal's importance to the research community. Many include counting the number of times the journal has been cited in other works. The differing formulas and methodology mean the results will differ from metric to metric. For example, an Eigenfactor score takes into consideration the size of the journal, allowing larger journals more weight, while other metrics do not take this into account. Comparing results from more than one metric will provide a better picture of the real impact of a journal.
While journal metrics are widely used in the academic and research community, they are not without controversy. These are a few articles for further reading that discuss some of the issues and challenges of measuring journal impact.