The total number of times that a journal has been cited by all journals included in the database in the JCR year.
Citations to journals listed in JCR are compiled annually from the JCR year’s combined database, regardless of which JCR edition lists the journal and regardless of what kind of article was cited or when the cited article was published. Each unique article-to-article link is counted as a citation.
Citations from a journal to an article previously published in the same journal are compiled in the total cites. However, some journals listed in JCR may be cited-only journals, in which case self-cites are not included.
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.
The impact factor is calculated by dividing the number of citations in the science citation index by the total number of articles published in the two previous years. An impact factor of 1.0 means that, on average, the articles published one or two year ago have been cited one time. An impact factor of 2.5 means that, on average, the articles published one or two year ago have been cited two and a half times. Citing articles may be from the same journal; most citing articles are from different journals.
The aggregate impact factor for a subject category is calcuted the same way as the impact factor for a journal, but it takes into account the number of citations to all journals in the category and the number of articles from all journals in the category. An aggregate impact factor of 1.0 means that that, on average, the articles in the subject category published one or two years ago have been cited one time. The median impact factor is the median value of all journal impact factors in the subject category.
The impact factor mitigates the importance of absolute citation frequencies. It tends to discount the advantage of large journals over small journals because large journals produce a larger body of citable literature. For the same reason, it tends to discount the advantage of frequently issued journals over less frequently issued ones and of older journals over newer ones. Because the journal impact factor offsets the advantages of size and age, it is a valuable tool for journal evaluation.
The impact factor trend graph shows the impact factor for a five-year period. To view the graph, click the Impact Factor Trend button at the top of the journal page.
The immediacy index is the average number of times an article is cited in the year it is published. The journal immediacy index indicates how quickly articles in a journal are cited. The aggregate immediacy index indicates how quickly articles in a subject category are cited.
The immediacy index is calculated by dividing the number of citations to articles published in a given year by the number of articles published in that year.
Because it is a per-article average, the immediacy index tends to discount the advantage of large journals over small ones. However, frequently issued journals may have an advantage because an article published early in the year has a better chance of being cited than one published later in the year. Many publications that publish infrequently or late in the year have low immediacy indexes.
For comparing journals specializing in cutting-edge research, the immediacy index can provide a useful perspective.
Journal Citing Half-Life
The citing half-life is the median age of articles cited by the journal in the JCR year. For example, in JCR 2003, the journal Food Biotechnology has a citing half-life of 9.0. That means that 50% of all articles cited by articles in Food Biotechnology in 2003 were published between 1995 and 2003 (inclusive).
Only journals that publish 100 or more cited references have a citing half-life. do not have a citing half-life.
The aggregate citing half-life is calculated the same way as the journal citing half-life, and its significance is comparable. For a subject category, the citing half-life is the median age of articles cited by journal in the category in the JCR year.
For example, in JCR 2003, the subject category Geochemistry & Geophysics has a citing half-life of 9.9. That means that 50% of all articles cited by articles in Geochemistry & Geophysics journals in 2003 were published between 1994 and 2003 (inclusive).
technorati tags:JCR, metrics, bibilometrics, citation data
Blogged with Flock
