Journal level metrics evaluate the impact of a particular publication by incorporating the number of times articles within that publication have been cited as part of a calculation. Each metric has its own formula for calculation and aims to provide a number to represent a particular aspect of impact.
Impact factor is the most frequently referenced journal level metric.
- "The journal Impact Factor is the average number of times articles from the journal published in the past two years have been cited in the JCR year." JCR stands for Journal Citation Reports. (http://admin-apps.webofknowledge.com/JCR/help/h_impfact.htm)
- "The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the two previous years." (http://admin-apps.webofknowledge.com/JCR/help/h_impfact.htm)
- Impact factors can also be calculated for 5-years. A 5-year impact factor "is calculated by dividing the number of citations in the JCR year by the total number of articles published in the five previous years." (http://admin-apps.webofknowledge.com/JCR/help/h_impfact.htm)
- Find impact factors using Journal Citation Reports.
Additional metrics have been developed to make up for some of the Impact Factor's shortcomings.
- Eigenfactor Score - "The Eigenfactor Score calculation is based on the number of times articles from the journal published in the past five years have been cited in the JCR year, but it also considers which journals have contributed these citations so that highly cited journals will influence the network more than lesser cited journals. References from one article in a journal to another article from the same journal are removed, so that Eigenfactor Scores are not influenced by journal self-citation." (http://admin-apps.webofknowledge.com/JCR/help/h_eigenfact.htm) Find an Eigenfactor Score using Journal Citation Reports or on the Eigenfactor website.
- SCImago Journal Rank (SJR) is "a measure of scientific influence of scholarly journals that accounts for both the number of citations received by a journal and the importance or prestige of the journals where such citations come from." (http://www.journalmetrics.com/sjr.php) Find SJR in Scopus or on Elsevier's Journal Metrics website.
- Source Normalized Impact per Paper (SNIP) is a metric that measures a journal's "contextual citation impact by weighting citations based on the total number of citations in a subject field." SNIP is the "ratio of the journal's citation count per paper and the citation potential in its subject field." (http://www.journalmetrics.com/snip.php) Find SNIP in Scopus or on Elsevier's Journal Metrics website.