Journal Impact Ratings
The following file is a set of 
Adobe
Acrobat files (*.pdf) providing the SSCI Impact Ratings for Journals
where articles on matters related to psychology are likely to be published. The
files are archived in zip format.
Journal
Impact Ratings for Psychology (2001)(896k)
Journal
Impact Ratings for Clinical Psychology 1999-2002 (534k)
Journal Impact Ratings for Psychology 2003 (760k)
How are impact ratings computed?
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 JCR
year 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.
Thus, the impact factor for the year 2004 for a given journal would be computed as follows:
2004 Impact factor = (# articles from 2003 cited + # articles from 2004 cited)/# articles published 2003 + # articles published 2004)
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.
Journal Cited Half-Life
The median age of the articles that were cited in the JCR year. Half of a journal's
cited articles were published more recently than the cited half-life. For
example, in JCR 2001 the journal Crystal Research and Technology has a cited
half-life of 7.0. That means that articles published in Crystal Research
and Technology between 1995-2001 (inclusive) account for 50% of all citations
to articles from that journal in 2001.
Only journals cited 100 or more times in the JCR year have a cited half-life.
A higher or lower cited half-life does not imply any particular value for a
journal. For instance, a primary research journal might have a longer cited
half-life than a journal that provides rapid communication of current information.
Cited half-life figures may be useful to assist in collection management and
archiving decisions. Dramatic changes in cited half-life over time may indicate
a change in a journal’s format. Studying the half-life data of the journals in a comparative study
may indicate differences in format and publication history.