Journal Impact Factor: What It Is, How is it Calculated and Where Can it Be Found
A couple of questions that consistently arise here at the library. One is how do you find the impact factor? Another is exactly what is an impact factor? Below I hope to be able to answer those questions for those who may be curious as to exactly what an impact factor measures, the debate over the usefulness of a impact factor when it comes to publications, and how you find the impact factor for a journal. Remember that if you any questions the librarians here at TML are here to help.
The JCR provides quantitative tools for ranking, evaluating, categorizing, and comparing journals. The impact factor is one of these; it is a measure of the frequency with which the "average article" in a journal has been cited in a particular year or period. The annual JCR impact factor is a ratio between citations and recent citable items published. Thus, the impact factor of a journal is calculated by dividing the number of current year citations to the source items published in that journal during the previous two years (see Figure 1).
Figure 1: Calculation for journal impact factor.
A= total cites in 1992
B= 1992 cites to articles published in 1990-91 (this is a subset of A)
C= number of articles published in 1990-91
D= B/C = 1992 impact factor
The impact factor is useful in clarifying the significance of absolute (or total) citation frequencies. It eliminates some of the bias of such counts which favor large journals over small ones, or frequently issued journals over less frequently issued ones, and of older journals over newer ones. Particularly in the latter case such journals have a larger citable body of literature than smaller or younger journals. All things being equal, the larger the number of previously published articles, the more often a journal will be cited.
(Taken from: Thomson reuters | the thomson reuters impact factor | science Retrieved 4/9/2013, 2013, from http://thomsonreuters.com/products_services/science/free/essays/impact_factor/)
2011 Impact Factor for American Journal of Critical Care
5-Year Journal Impact Factor
Factors that Influence Impact Factors
Date of Publication:
The impact factor is based solely on citation data and only looks at the citation frequency of articles from a journal in their first couple years of publication. Journals with articles that are steadily cited for a long period of time (say, 10 years) rather than only immediately lose out with this calculation.
Large vs. Small Journals:
Large and small journals are compared equally. Large journals tend to have higher impact factors--nothing to do with their quality.
It's important to remember that the impact factor only looks at an average citation and that a journal may have a few highly cited papers that greatly increase its impact factor, while other papers in that same journal may not be cited at all. Therefore, there is no direct correlation between an individual article's citation frequency or quality and the journal impact factor.
Impact factors are calculated using citations not only from research articles but also review articles (which tend to receive more citations), editorials, letters, meeting abstracts, and notes. The inclusion of these publications provides the opportunity for editors and publishers to manipulate the ratio used to calculate impact factor and falsely try to increase their number.
Changing / Growing Fields:
Rapidly changing and growing fields (e.g. biochemistry and molecular biology) have much higher immediate citation rates, so those journals will always have higher impact factors than nursing, for instance.
ISI's Indexing / Citation Focus:
There is unequal depth of coverage in different disciplines. In the health sciences, the Institute for Scientific Information (ISI), the company which publishes impact factors, has focused much of their attention on indexing and citation data from journals in clinical medicine and biomedical research and has not focused on nursing as much. Very few nursing journals are included in their calculations (around 45). This does not mean that nursing journals they do not include are of lesser quality, and, in fact, they do not give any explanation for why some journals are included and others are not. In general, ISI focuses more heavily on journal dependent disciplines in the sciences and provides less coverage for areas of the social sciences and humanities, where books and other publishing formats are still common.
Research vs. Clinical Journals
In some disciplines such as some areas of clinical medicine where there is not a distinct separation between clinical/practitioner versus research journals, research journals tend to have higher citation rates. This may also apply to nursing.
(Taken from: Home - journal impact factors - guides at michigan state university libraries Retrieved 4/9/2013, 2013, from http://libguides.lib.msu.edu/impactfactors )
How to Find a Journal's Impact Factor
- Go to the Tompkins-McCaw Library Website and click on Web of Science under search collections.
- On the Web of Science page go to the tabs at the top of the page and click on the one that says select a database.
- Select Journal Citation Reports®
- Select the JCR edition (Science or Social Science) and year that you want. When it comes to some subjects the subject appears under both editions. Nursing is one subject that appears in both editions.
- Next, select a search option (view journals by subject, search for a specific journal, or view all journals) to find if the journal you're looking for has an impact factor.
- In order to see how the journal you are interested in compares to other in a particular field, it is best to select "view a group of journals by subject category" and click submit.
- Select the topic/category you want to see from the list (You can select more than one by holding down the Ctrl key and clicking on multiple categories). Below this list of categories you can select how you would like to view the journals by going to the drop down menu and choosing accordingly.
Articles: Impact Factor Debate
- Citations are hotlinked to the article. You will need to either be on campus or authenticate in order to access them.