Below is a quick summary of what to expect from the three primary citation analysis tools. In addition to these tools, click on the tab Web Based Resources to see additional databases which also offer citation searching features.
Web of Science |
Scopus |
Google Scholar |
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| Subject Focus |
Science, Technology, |
Science, Technology, Medical, Engineering, Arts & Humanities | Medical, Scientific, Technical, Business, Social Sciences, Arts & Humanities |
| Components |
Composed of:
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| Coverage | Over 11,000 journals | Over 18,000 journals | Unknown |
| Time Span | Some journal files going back to 1900 |
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Theoretically, whatever is available on the Web |
| Updated | Weekly | 1-2 Times a week | Monthly on average |
| Strengths |
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| Weaknesses |
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Definition
The impact factor (IF) is a citation measure produced by Thompson Scientific's ISI Web of Knowledge database. Impact factors are published annually in ISI's Journal Citation Reports Database. Impact factors are only available for journals that are indexed in ISI databases. IF is one measure of the relative importance of a journal, individual article, or scientist to science and social science literature and research. Each index or database used to create an impact factor uses a different methodology and produces slightly different results, revealing the importance of using several sources to judge the true impact of publishing in a particular journal or of a scientist's work.
Informed and careful use of these impact data is essential, and should be based on a thorough understanding of the methodology used to generate impact factors.
One journal's impact factor on its own doesn't mean much. Instead, it's important to look at impact factors of multiple journals in the same subject area. This way, one can determine if the impact factor of the journal of interest is high or low compared to other journals in the same subject area.
Impact Factor Debate
Impact factors have been much debated in the literature in terms of their value for evaluating research quality. The general consensus is that impact factors have been misunderstood and abused by many institutions that place too much value on something that is not entirely scientific or reliable. Also, many faculty tenure and promotion's committees and college/university administrators use IFs for purposes for which the IF was not designed, thereby misusing the IF information and unfairly judging a faculty member's contribution. Listed below are some of the issues concerning IFs:
It is not clear whether the number of times a paper is cited measures its actual quality.
Some databases that calculate impact factors fail to incorporate publications including textbooks, handbooks and reference books.
Certain disciplines have low numbers of journals and usage. Therefore, one should only compare journals or researchers with the same discipline.
Review articles normally are cited more often and therefore can skew results.
Self-citing may also skew results.
Some resources used to calculate impact factors have inadequate international coverage.
How Impact Factors are Calculated
A journal's impact factor for 2007 would be calculated by taking the number of citations in 2007 to articles that were published in 2006 and 2005 and dividing that number by the total number of articles published in that same journal in 2006 and 2005. Please see the example below.
Example:
The specific calculations for Nursing Research's 2007 impact factor are displayed below.
Articles published in 2006 that were cited in 2007: 98
Articles published in 2005 that were cited in 2007: 103
98+103=201
Total Number of articles published in 2006: 67
Total number of articles published in 2005: 48
67+48=115
201 (articles published in 2006 and 2005 that were cited in 2007)
115 (total number of articles published in 2006 and 2005)
= 1.748
The 2007 Impact Factor for the journal Nursing Research means that, on average, articles published in this journal from one or two years ago have been cited around 1 and three-quarter times.
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.
Average Citation
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.
Review Articles
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. The Institute for Scientific Information (ISI), the company which publishes impact factors in the health sciences, 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.
This map from Eigenfactor.org shows how science/medicine areas are interconnected to each other. See their website below for more information and different kinds of mapping displays. Orange circles represent fields, with larger, darker circles indicating larger field size as measured by Eigenfactor score™. Blue arrows represent citation flow between fields. An arrow from field A to field B indicates citation traffic from A to B, with larger, darker arrows indicating higher citation volume. (From www.eigenfactor.org)