OSA Library Resource Center
Welcome to the new OSA Library Resource Center. Recognizing your need to have data at your finger tips, we have developed some critical resources to help you better manage your subscriptions to OSA publications. These resources include access to COUNTER compliant and other related usage statistics, your current account information, access to your institution's subscription history, as well as a view into the personalized My InfoBase service as seen by your patrons.
Should you have any questions about your institution's subscriptions or require any assistance with this service center, please do not hesitate to contact us at firstname.lastname@example.org or +1.202.416.1901.
OverviewThere are many different journal evaluation metrics produced by several companies, each using different sets of data and time periods for their calculations. Most metrics, and all the metrics discussed below, focus on value for scientific and academic research (citations) and do not take into account other ways content is used (e.g. industrial and commercial applications). The below guide is meant to help authors and readers better understand some of the common metrics used to evaluate journal content.
Thomson Reuter's Journal Citation Reports (JCR) Metrics:Date range: varies Data source: journals indexed in Thomson Reuter's Web of Science.
Impact Factor: A metric meant to indicate the number of times the "average" article in the journal is cited. This number is the most widely used metric to evaluate a journal's content. The metric is based on citations in a particular year to articles published over the previous two years. An example of how an Impact Factor is calculated is below.
Source: Thomson Reuters Journal Citation Reports—Optics Express 2012 Impact Factor calculation
- Total Citations: This is the number of total citations in a given year to all content ever published in a specific journal.
- Immediacy Index: a measure of how quickly the "average article" in a journal is cited. The Immediacy index will tell you how often articles published in a given year are cited within the same year.
- Cited Half-life: This figure is the median age of the articles cited in the given year. For example, in JCR 2012, Optics Letters has a cited half-life of 6.5 years. That means that articles published in Optics Letters between July 2006 and December 2012 account for 50% of all citations to Optics Letters articles in 2012.
- Eigenfactor Score: a metric based on the number of times articles from the journal published in the past five years have been cited in the current 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.
- Article Influence: determines the average influence of a journal's articles over the first five years after publication. It is calculated by dividing a journal's Eigenfactor Score by the number of articles in the journal, normalized as a fraction of all articles in all publications. The mean Article Influence Score is 1.00. A score greater than 1.00 indicates that each article in the journal has above-average influence. A score less than 1.00 indicates that each article in the journal has below-average influence.
- Impact Factor: A metric meant to indicate the number of times the "average" article in the journal is cited. This number is the most widely used metric to evaluate a journal's content. The metric is based on citations in a particular year to articles published over the previous two years. An example of how an Impact Factor is calculated is below.
Date range: Previous three years of data
Data source: Journals indexed in Elsevier's SCOPUS database
(OSA titles include: Advances in Optics and Photonics, Applied Optics, Applied Spectroscopy, Biomedical Optics Express, Chinese Optics Letters, Journal of Display Technology, Journal of Lightwave Technology, Journal of Optical Communication and Networking, JOSA A, JOSA B, Journal of the Optical Society of Korea, Journal of Optical Technology, Optical Materials Express, Optics Express, and Optics Letters)
- SCImago Journal Rank (SJR): a metric based on a random-walk model. It calculates the percentage of time a researcher would spend reading content from each journal if they randomly followed references from one article to another. An SJR of two means that two percent of the researcher's time is spent reading this particular journal.
- Source Normalized Impact per Paper (SNIP): measures a source's contextual citation impact. It takes into account characteristics of the source's subject field, especially the frequency at which authors cite other papers in their reference lists, the speed at which citation impact matures, and the extent to which the database used in the assessment covers the field's literature. A value that is higher than one means that the journal has an above average SNIP for its field. A SNIP that is lower than one means that the journal has a below average SNIP for its field. If SNIP = 1, the journal is absolutely average for its field. Notes: SNIP and SJR only consider citations made by peer-reviewed content and directed to peer-reviewed content.
Date range: articles published between 2008 and 2012 and citations as of July 2013.
Data source: all articles indexed in Google Scholar.
- h-index: The h-index of a publication is the largest number h such that at least h articles in that publication were cited at least h times each. For example, a publication with five articles cited by, respectively, 17, 9, 6, 3, and 2, has the h-index of 3.
- h-core: The h-core of a publication is a set of top cited h articles from the publication. These are the articles that the h-index is based on. For example, the publication above has the h-core with three articles, those cited by 17, 9, and 6.
- h-median: The h-median of a publication is the median of the citation counts in its h-core. For example, the h-median of the publication above is 9. The h-median is a measure of the distribution of citations to the articles in the h-core.
- Finally, the h5-index, h5-core, and h5-median of a publication are, respectively, the h-index, h-core, and h-median of only those of its articles that were published in the last five complete calendar years.