The World’s Most Trusted Citation Index Covering the Leading Scholarly Literature.
The Science Citation Index (now the Science Citation Index Expanded, or SCIE) is one of the core databases included in the products Web of Knowledge and Web of Science, owned by Thomson Reuters (http://ipscience.thomsonreuters.com/product/web-of-science/). In fact, Web of Science comprises a number of database resources, and the journals covered are subject to an evaluation process before inclusion. Publishers wishing to get their journals evaluated need to submit a proposal to a committee which oversees the Web of Science Core Collection Journal Selection Process. The evaluation takes into consideration a number of criteria, and it is notable that these include not just analysis of the citations to its content, but also factors such as the editorial process and adherence to good publishing practices (e.g. in relation to the peer review process and timeliness of publication) and also the scope and international provenance of the journal.
Statistics from Thomson Reuters show that about 3500 journals are evaluated annually, and around 10% will be selected for inclusion. Once included, the ‘citation impact’ is published annually in the summer detailing the Journal Impact Factor of those journals included.
The first ‘impact factors’ were published in 1975. Impact factors are published in an annual report known as the Journal Citation Reports (JCR), which is part of the Web of Science portfolio.
What is an ‘impact factor’
The impact factor is a measure of the citations published within a given journal over a fixed time period. Specifically, it reflects the average number of citations for each paper published in a journal during the two preceding years. So:
Where A= total citations in 2014
B= 2014 citations to articles published in 2012-13 (this is a subset of A)
C= number of articles published in 2012-13
D= B/C = 2014 impact factor
Note that new journals need to wait 2 years before they can be evaluated and given an impact factor [there are some occasional exceptions to this, where impact factors based on partial data will be given].
There can be factors that influence the impact factor, such as the publication of review articles (which naturally tend to include higher levels of citations to earlier literature).
Self-citation can also influence the metrics, but note that the Journal Selection Process takes this into consideration, and artificially high levels of deliberate self-citation will affect the selection process.
Scopus is an interdisciplinary citation database of peer-reviewed literature, featuring smart tools to track, analyze and visualize research. Scopus includes Medline as well as most of the references in Embase.
Scopus claims to be the largest abstract and citation database of peer-reviewed literature (mostly journals) with bibliometrics tools to track, analyze and visualize research.
Content
To keep track of what's happening in your research world, turn to Scopus. Across all research fields — science, mathematics, engineering, technology, health and medicine, social sciences, and arts and humanities — Scopus delivers the broadest overview of global, interdisciplinary scientific information. Content on Scopus comes from over 5,000 publishers and must be reviewed and selected by an independent Content Selection and Advisory Board (CSAB) to be, and continue to be, indexed on Scopus.
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What is the difference between an SCI & SCIE?
The Science Citation Index (SCI) is a sub-set of the Science Citation Index Expanded (SCIE), containing journals that rank competitively among the most highly-cited core journals in their category or categories. The Science Citation Index Expanded is essentially the web version of what used to be a database available only on CDRom/Diskette.
When selecting the journals for the Science Citation Index we choose the top journals from each subject category and supplement this with top regional journals from each category to give broad geographic and multidisciplinary coverage. The evaluation of and acceptance of a journal for the Science Citation Index Expanded or the Science Citation Index is essentially the same with one major difference.
This difference is in the application of citation analysis to the journal. While every science journal in the database is covered in the Science Citation Index Expanded and only those journals of relatively significantly higher citation impact are selected for the Science Citation Index. In other words, Science Citation Index covers only the most highly cited, highest impact journals in each category. This is because of the constraints of the CDROM and print media there is no difference in the selection process for Science Citation Index and Science Citation Index Expanded journals.