Journal Citation Reports (JCR), SCImago Journal & Country Rank (SJR), Essential Science Indicators
The databases mainly offer information on the basis of citation analysis of journals, subject areas and countries and can be used, for example, to check the relative significance of journals within a subject category or - as an author - to select journals for future publications or to evaluate existing publications.
JCR (with Impact factor)
In the Journal Citation Reports Science Edition database of the American company Thomson, the article and citation data of more than 8000 mainly English-language journals from the fields of medicine, technology and science are evaluated each year. There is also the JCR Social Sciences Edition. The data is published each year in July (online and on CD-ROM) and is based on the evaluations of the previous year (JCR year).
Note: If you select the Search for a specific journal option, you should bear in mind that when you search with title abbreviations, the Abbreviated Journal Titles in JCR do not always match other abbreviations. To be on the safe side, you can search using the Full Journal Titles that are linked as a list.
Journal impact factor
The journal impact factor indicates how frequently the "citable" articles of a certain journal were cited on average in the two years before the JCR year. An impact factor of 1.0 means that, on average, each citable article of the previous two years was cited once. Citing articles may be from the same journal.
Example for journal X in JCR year 2006:
| IF = | Number of citations from 2006 to journal X in the 2 previous years |
| Number of citable articles of journal X in 2004 and 2005 |
Note: "Citable articles" in the denominator are usually research articles and reviews. In the numerator, on the other hand, the citations of all document types of JCR journals are also counted amongst the non-citable document types, such as editorials, letters, news items and meeting abstracts.
5-Year Journal Impact Factor
This value was introduced with JCR 2007 - the time window for citable articles has been extended from 2 to 5 years.
Aggregate and median impact factor
The "aggregation" groups journals according to subject categories and is calculated in the same way as the journal impact factor, but takes into account all journals of a subject category. The median applies to all journal impact factors of the subject category.
The Association of the Scientific Medical Societies in Germany (AWMF) provides the median impact factors of the subject categories on their website as Median impact factors (in German).
Impact factor trend
A graph shows the journal impact factor trend over the last 5 years.
In Web of Science, you can display this value from the detailed display using the "View record in Journal Citation Records" link.
Comments on the impact factor
In order to properly assess the value of impact factors, you have to consider a number of conditions and weaknesses:
- The impact factor is not necessarily a measure of the quality or perception of a particular article, as relatively few articles in a journal contain the majority of citations.
- Impact factors vary from one subject category to another within medicine and cannot be compared directly as, for example, large or rapidly-growing specialist disciplines have more researchers and publication organs.
- The JCR journals are selected purely by the database producer. Mainly English-language journals are evaluated. Many German-language journals with peer reviews are not included in the JCR.
- Non-English-language journals have a relatively lower IF, as the coverage in the JCR is low and they attract less attention worldwide due to language barriers.
- Journals whose articles are regularly cited for significantly longer than two years (longer half-life), are rated comparatively lower, see Cited half-life.
- New branches of research are cited less frequently.
- Basic research is rated higher than clinical medicine, as clinical medicine draws heavily on basic research.
- Many citations to non-citable document types increase the IF.
- Journals with a large proportion of reviews may have a comparably higher IF, as reviews are, on average, cited more frequently than research papers.
- Journals with free access to full-text articles (Open Access) have a comparatively high IF.
(IF of BioMed Central journals, Open Access in medicine.)
Most of the issues mentioned here are taken from the article by Dong; Loh; Mondry: The "impact factor" revisited (published on 05.12.2005). Other issues are listed there.
AWMF proposals for the use of the impact factor (May 2000)
- Not suitable for use in assessing individuals during "Habilitation" (post-doctoral professorships) and "Berufung" (appointments as professors), but instead exclusively for the internal distribution of research funds in institutes/research groups
- Impact factors of individual journals should be evaluated according to subject by dividing them by the average impact factors of the subject categories (median).
- The impact factor for German-language journals listed in JCR should be doubled.
- Original papers from specialist journals that are not listed in JCR should be rated with an "equivalent impact factor" of 0.2.
- Articles in textbooks and manuals or monographs are given alternative impact factor scores, similar to journal publications.
For more detailed information, see AWMF proposals for the use of the "impact factor" (in German)
Eigenfactor
Two new evaluation criteria were developed at the University of Washington on the basis of JCR data, to rank JCR journals according to their influence or importance. The values are described at eigenfactor.org, for legal reasons they are accesible from december on for the previous year - and they are accesible starting with JCR 2007 in JCR.
Among other things the calculation considers the prestige of a journal. There is a 5 year window for the analysis of the citations. Self citations are filtered out.
The Article Influence score is a value for the average influence of articles of a journal and is therefore comparable with the journal impact factor. It is calculated with the Eigenfactor score divided by the normalized part of the articles of a journal. The median AI score is 1.
The Eigenfactor score is a value for the influence of a journal on the scientific community. It should be a measure for the time slice a user spends reading a journal. The total value of all Eigenfactor scores of the JCR journals is 100.
Other JCR values
Other indicators are calculated in the JCR both for individual journals and for individual subject categories. Some of these include:
Immediacy index
The "journal immediacy index" tells you how often articles published in a specialist journal are cited on average within the same year. It is calculated by dividing the number of citations in a particular year by the number of articles of the same year. Citing articles may be from the same journal.
The "aggregate immediacy index" is the value for one subject category.
Cited half-life
Cited half-life of a journal: Half of the citations to a particular journal refer to articles that were published within the year value calculated (counted backwards from the JCR year).
For example: Journal X has a value of 7.0 years in the JCR year 2006. This means that 50% of all citations, which refer to journal X, were between 2000 and 2006 (inclusively).
The "aggregate cited half-life" is the value for one subject category.
The higher the value, the greater the average half-life of an article. Less modern or less fast-moving subject categories, in which the citation maximum is only reached after more than 2 years can, in some situations, compensate for a lower impact factor with a higher half-life by multiplying the two values, see Description of the impact factor in Wikipedia (accessed on 10.09.08).
Citing half-life
Citing half-life of a journal: Half of the citations in a journal refer to articles that were published within the year value calculated (counted backwards from the JCR year).
For example: Journal X has a value of 7.0 years in the JCR year 2006. This means that 50% of all articles, which were cited from articles of journal X, were published between 2000 and 2006 (inclusively).
The "aggregate citing half-life" is the value for one subject category.
SCImago Journal & Country Rank
This free database (Scimagojr.com) offers among other things the value SCImago Journal Rank (SJR, since 1999), which is comparable with the IF, but includes a consideration of the prestige of a journal. The basis is the database SCOPUS (competing product to Web of Science), which analyzes more journals than JCR/WoS. There is a 3 year window for the analysis of the citations. Self citations are filtered out. The data are updated yearly in November.
Via the Journal display you can see some values for subject areas or individual journals like the average citaton per document, the amount of uncited documents or the rate of international collaboration.
With the Country Rank you can analyze separate countries and 10 world regions - the values are e.g. the amount of publications, average citations per publication, self citations, uncited documents and the h index (number of publications (h) that have been cited at least h times).
The Compare function enables the comparison of a maximum of 4 countries or world regions according to subject areas, or of a maximum of 4 journals.
With the Map Generator you can compare e.g. the subject categories in medicine by bubble charts according to different criteria.
Essential Science Indicators (ESI)
ESI
offers e.g. citation rates (Citations per Paper) according to persons, institutions, countries and journals - always restrictable via a rough subject classification, (e.g. Clinical Medicine, see Field List). Highly Cited Papers (last 10 years) and Hot Papers (last 2 years) are selectable with the same criteria.
Via the link Baselines, the average citation rates and percentiles according to separate years (since 1999) and the total citation rates are shown - always according to subject areas.
Research Fronts group (according to subject areas) often cited publications (Core Papers) to special topics.
On the article level there is always a link to Web of Science.
Access options
- Dong; Loh; Mondry: The "impact factor" revisited. 2005
- Ball; Tunger: Bibliometrische Analysen - Daten, Fakten und Methoden - Grundwissen Bibliometrie für Wissenschaftler, Wissenschaftsmanager, Forschungseinrichtungen und Hochschulen. 2005
- Glänzel; Debackere: Bibliometrie zwischen Forschung und Dienstleistung. In: Ball (Hrsg.): WissKom 2007 : Wissenschaftskommunikation der Zukunft ; 4. Konferenz der Zentralbibliothek, Forschungszentrum Jülich, 6. - 8. November 2007, Beiträge und Poster. 2007, P. 209-222
- Bauer B.: Habilitationskriterium Impact Factor - Wie evaluieren medizinische Fakultäten wissenschaftliche Leistungen von Habilitanden? 2003
- Essays on JCR and IF at Thomson Scientific
- The Thomson Scientific Journal Selection Process
