| Citation
and Article Counts |
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Citation and article counts are important indicators
of how frequently current researchers are using
individual journals. By tabulating and aggregating
citation and article counts, the JCR offers a unique
perspective for journal evaluation and comparison.
Citation counts. The formal acknowledgment of
intellectual debt to previously-published research,
publicly recorded in the references listed by
contemporary authors.
 | Total citations (listed in the Total
Cites column in the Journal Rankings Window)
indicates the total number of times that each
journal has been cited by all journals included in
the ISI database within the current product year.
| Compiling total citations. Citations
to journals listed in the JCR are compiled
annually from the current 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. For example, a single article may give 40
references, but if only 35 different articles are
cited in those 40 references, it is the 35 unique
citations that are distributed among the cited
journals.
| Self-Citations. Citations from a
journal to an article previously published in the
same journal are compiled in the total cites.
However, some journals listed in the JCR may be
cited-only journals, in which case self-cites are
not included.
| We have, in compiling the JCR, refrained from
combining data on the basis of lineage, except where
a title change has been so minor that it does not
affect the title's position alphabetically. Nor does
the JCR combine data for "sections" of the
"same" journal. It is up to the user to
decide whether or not one’s purpose recommends
that counts be combined. A list of journal title
changes for the past two years is provided to assist
your efforts. Citations are unified in the case of
journals that publish both an original language
edition and a cover-to-cover translation. These
journals are marked with a plus sign (+). |
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Article counts
(current articles). The number of articles published
in a journal in a particular year or years. Editorials,
letters, news items, and meeting abstracts are not
included in article counts because they
are not generally cited (see Using
the JCR Wisely).
| Current year articles (listed in the
Articles column in the Journal Rankings Window)
shows the number of articles published in each
journal in the current product year. A reasonable
effort is made to include a full year’s issues for
journals covered in the ISI database. However, it is
necessary for material to be processed by
mid-February each year for inclusion in the JCR.
| Previous year articles (listed in the Full
Journal Record under the link to the impact factor
calculation), shows the number of articles published
in each of the previous two years, and the sum,
which is used to calculate the impact factor. |
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| Cited
Half-Life |
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The cited half-life is the number of publication
years from the current year which account for 50% of
current citations received. This figure helps you
evaluate the age of the majority of cited articles
published in a journal. Each journal’s cited half-life
is shown in the Journal Rankings Window. Only
those journals cited 100 or more times have a cited
half-life.
The chronological distribution of the cumulative
percent of citations received per publication year is
shown in the Cited Half-Life Calculation dialog box.
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-Lifes 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.
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| Cited
Journal Listing |
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The JCR specifically identifies those publications
that most frequently cited a particular journal. These
citation links can reveal a journal’s
subject orientation, point to its closest peer or
competitor publications, and describe specialty-specific
networks of journals.
From each journal's Full Record page, you can access
its Cited
Journal Page to view a table of journals whose
articles cited those in the journal you are
investigating.
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| Cited-Only
Journals (Journals with only Cited Journal information) |
| Some of
the journals listed in the JCR are not citing
journals, but are cited-only journals. This means that
the references in these journals are not included in the
ISI database. This is significant when comparing
journals, because self-citations from cited-only
journals are not included in the JCR data.
Self-citations often represent a significant percentage
of the citations that a journal receives. The cited-only
journals may be ceased journals, suspended journals,
superseded titles. Any journal that appears elsewhere in
the JCR, but not in the Citing Journal Listing, is a
cited-only journal. |
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| Citing
Half-Life |
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The citing half-life is the number of publication
years from the current year that account for 50% of the
current citations published by a journal in its article
references. This figure helps you evaluate the age of
the majority of articles referenced by a journal.
The chronological distribution of the cumulative
percent of citations given out is shown in the Citing
Half-Life Calculation dialog box. Only those journals
publishing 100 or more citations have a citing
half-life. Cited-only
journals do not have citing half-lifes.
Dramatic changes in Citing Half-Lifes 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.
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| Citing
Journal Listing |
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The JCR specifically identifies those publications
that were most frequently cited by a particular
journal. These citation links can reveal a
journal’s subject orientation, point to its
closest peer or competitor publications, and describe
specialty-specific networks of journals.
From each journal's Full Record page, you can access
its Citing
Journal Page to view a table of journals whose
articles were cited by those in the journal you are
investigating.
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| Immediacy
Index |
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The journal Immediacy Index is a measure of
how quickly the "average article" in a journal
is cited. The Immediacy Index will tell
you how often articles published in a journal are cited
within the same year.
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.
The Immediacy Index is useful in comparing how
quickly journals are cited. 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 here,
because an article published early in the year has a
better chance of being cited than one published later in
the year. For comparing journals specializing in
cutting-edge research, the Immediacy Index can provide a
useful perspective (see How
to Find the Hottest Journals).
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| Impact
Factor |
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The journal impact factor is a measure of the
frequency with which the "average article" in
a journal has been cited in a particular year. The
impact factor will help you evaluate a journal’s
relative importance, especially when you compare it to
others in the same field.
The impact factor is calculated by dividing the
number of current citations to articles published in the
two previous years by the total number of articles
published in the two previous years.
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| Journal
Title Changes |
| A listing
of journal title changes are provided on the Journal
Title Changes page for all changes occurring in the
past two years (the JCR edition year and the preceding
year). The listing is in alphabetical order by journal
title. |
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| Self-Citations |
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Self-citations are when a journal article references
articles from that same journal. Self-citations often
make up a significant portion of the citations a journal
gives and receives each year. You can compare self-citing
rates and self-cited rates to supplement your
journal evaluation. Refer to Analyze
Self-Citations for more information.
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| Source
Data |
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The Source Data table details the number of articles
published in the current year by the journal, the total
number of references contained in those articles,
and the average number of references per article. The
article counts given for journals include only original
research and review articles. Editorials, letters, news
items, and meeting abstracts are not counted, because
they are not generally cited (see Using
the JCR Wisely). Cited-only
journals that appear in the JCR have no Source Data.
The Source Data Listing not only shows the ratio of
cited references to all articles published by the
journal (in the "Combined" column), it also
gives you the average number of references in each
"nonreview" (original research) and review
article. This permits you to see which journals
published reviews and how many they published.
Review articles are often more highly cited than
original research articles. Articles are coded as
"reviews" if they have more than 100
references, if they appear in review publications or
review sections of journals, if they have the word
Review or Overview in their titles, or if the summary
states that the article is a review or a survey.
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| Subject
Categories |
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Each journal in the ISI database is assigned to at
least one subject category (or discipline), indicating a
general area of science or the social sciences. Journals
may be included in more than one subject category;
therefore, when comparing journals across related
categories, it is possible to see the same journal title
in different categories.
Subject categories can be used to help hone your
searches. For example, it may be important to you to
make a distinction between a journal’s overall
rank and its rank within a particular subject category.
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| Total
Cites |
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Total Cites is the number of total citations to
articles in the journal for the current JCR year.
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