Bibliometrics (the measurement of scholarly citation) has long been dominated by the Science Citation Index. Created by Eugene Garfield in the 1960s, the SCI is now made available online as Web of Science by Thomson Scientific. In the last few years however two new services, Scopus and Google Scholar, have created competition for Web of Science, providing an alternative means to discover which articles have cited a particular research article. Scopus, a paid for service, offers an attractive user interface that is arguably easier to use and in some ways more powerful than that of Web of Science, while Google Scholar, though more limited in functionality, has the
significant benefit of being free.

Until very recently, though, one area of Thomson Scientific’s monopoly has remained essentially unchallenged – that of journal metrics. Thomson’s Journal Citation Reports service (JCR), whilst frequently criticized, has been the unchallenged de facto standard for the comparison of journals, and the “impact factor” metric used in the JCR to rank journals has acquired almost mystical importance within the scientific community as a measure and signifier of the kudos associated with publication in a particular journal. For this reason, the announcement of SCImago Journal and Country Rank, a alternative database of journal citation metrics developed by researchers in Spain,
is highly significant for the communication and evaluation of scholarly research.

Unlike the JCR (which is available to subscribers only), SCImago is freely available online, but in addition to being free, SCImago offers important improvements, compared to the JCR:

• Perhaps the most fundamental improvement, compared to the JCR, is the breadth of SCImago’s scientific, technical and medical journal coverage. SCImago makes use of data supplied by Scopus which covers 13,000 journals, including many STM journals not tracked by Thomson Scientific. Thomson Scientific often wait several years before including new journals in, and in some cases (see below) may not track journals at all, even though they are highly cited. As a result of this, although those BioMed Central’s journals which are listed in the JCR have impressive impact factors, many other high calibre BioMed Central journals are not currently listed in the JCR. In contrast, Scopus has a more systematic policy on content inclusion and adds all new BioMed Central titles to its database on an annual basis, and so SCImago contains reliable bibliometric data and rankings for around 100 BioMed Central journals that are not yet listed in the JCR.
• The SCImago Journal Rank (SJR) is used as an alternative to the impact factor, as the primary measure of a journal’s citation impact. One of the major criticisms of the impact factor algorithm is that it gives equal weight to all citations – a citation from a very obscure journal is weighted as being just as important as a citation that occurs in the New England Journal of Medicine, or Nature.
• This is a problem, as it seems intuitively clear that a citation from a journaL that is itself highly cited is a more reliable and significant indicator of importance and impact. To address this weakness, SCImago have taken the mathematical approach behind the PageRank algorithm that has been central to Google’s success as an internet search engine, and have adapted it to journal metrics in order to create the SCImago Journal Rank. The PageRank-style approach weights citations from journals according to how highly cited the journal itself it, using an iterative approach. Details of the SJR algorithm are available here.
  [SCImago is not the first group to apply a PageRank style algorithm to bibliometrics – Eigenfactor.org launched last year with a similar approach, and the Eigenfactor.org methodology page provides a good overview of the mathematical background and previous work in this area. However, because Eigenfactor.org relies solely on Thomson Scientific data, it does not offer the same breadth of coverage of new open access journals as SCImago].
• One additional point of note is that while impact factors are derived from citations in a single year to articles from the two preceding years, the SJR calculation looks at citations made in a three year period, of articles
  published in an earlier, but overlapping, three year period. This makes the SJR a more stable indicator of trends than impact factors, which often fluctuate substantially from year to year.

How do SJR rankings for BioMed Central journals compare with JCR rankings?

The SJr algorithm, combined with the more comprehensive pool of citation data provided by Scopus, leads to many significant changes in the relative ranking of journals. A few examples of this are identified below:

• Genome Biology is ranked 54th of all the 13,000+ journals listed by SCImago, outranking journals such as PLoS Biology (which is ranked 60th). In fact, excluding review journals, Genome Biology is the 29th most highly ranked title in SCImago, putting it in an elite club of the most influential research journals.
• Arthritis Research & Therapy is ranked 2nd of 37 in Rheumatology by SCImago, outranking journals such as Annals of Rheumatic Disease, Current Opinion in Rheumatology, Rheumatology, and Osteoarthritis and Cartilage even though those journals have higher impact factors according to the JCR.
• Breast Cancer Research, which ranks 26th of 139 journals in Cancer Research similarly leapfrogs its competitor Breast Cancer Research and Treatment (which is ranked 43rd in this category).

What about BioMed Central journals that are not yet listed in the JCR?

Here are a few examples of the journal metric data available from SCImago for BioMed Central journals which do not yet have official impact factors:

• Journal of Biology, which Thomson Scientific strangely do not track due to its small publication volume, confirms its status as a journal of the very highest quality. It ranks 44th of all 13,000+ journalss in SCImago (21st if review journals are excluded).
• BMC Biology, the flagship biology journal in the BMC-series, ranks 227th
  of all 13,000+ journals listed in SCImago – i.e. one of the top 2% (BMC Biology is expected to receive
  its first impact factor in June 2008)
• BMC Medicine, the flagship medical title in the BMC-series, is ranked 3rd
  of 241 titles in SCIMago’s Public Health, Environmental and Occupational Health category and 532nd in the overall database – a very high ranking for a medical journal.  (BMC Medicine was recently accepted for
  tracking by Thomson Scientific, but will not appear in the JCR until June 2009)
• BMC Medical Education, not yet accepted for tracking by Thomson Scientific, ranks 14th of the  249 journals in SCImago that include ‘Education’ in their title. (i.e. it is one of the top 6% of such journals)
• Retrovirology, due to receive its first impact factor in June 2008, ranks 5th of 46 in Virology.

Update 04-Jun-2008

Some further notable SCImago rankings

• Molecular Pain, due to receive its first impact factor in June 2008, ranks 1st of 87 in Anesthesiology and Pain Medicine
• Frontiers in Zoology ranks 4th of 235 in Animal Science and Zoology
• Theoretical Biology and Medical Modelling ranks 2nd of 24 in Health Informatics
• International Journal of Behavioral Nutrition and Physical Activity, Nutrition & Metabolism, and Nutrition Journal rank 1st, 2nd and 4th of 30 respectively, in Nutrition and Dietetics
• BMC Biotechnology ranks 7th of 141 in biotechnology
• BMC Plant Biology is not currently classified under Plant Science but has an SJR that would place it 10th of 274 in this area