Name: Journal Impact Factor
Can apply to: Journals selected for indexing by Journal Citation Reports
Metric definition: The Journal Impact Factor is a measure reflecting the annual average number of citations to recent articles published in that journal.
Metric calculation: From Wikipedia: “In any given year, the impact factor of a journal is the number of citations received in that year by articles published in that journal during the two preceding years, divided by the total number of articles published in that journal during the two preceding years.”
Data sources: Thomson Reuters Journal Citation Reports
Appropriate use cases: The JIF can be useful in comparing the relative influence of journals as measured by citations. Used appropriately and in conjunction with other metrics, the JIF can be useful in collection development decisions made by librarians.
Limitations: The widespread use of the JIF has resulted in its corruption through gaming by journal editors, perverting incentives, and misuse as a measure of the quality or impact of individual scholars or articles. Here are the most commonly noted limitations of the JIF:
- There is a lack of transparency about the database of journal articles on which the JIF is calculated. More specifically, Thomson Reuters does not provide clear, concrete guidelines for the journals and article types selected for inclusion.
- In some disciplines, 2 years is not enough time for articles to accrue citations.
- Many journals, particularly in the arts and humanities, are not covered by the Journal Citation Reports, which is the source of the JIF.
- There is a strong English language bias in the journals covered.
- There is a strong American bias in the journals covered.
- The JIF is affected by many cultural differences across disciplines (e.g., frequency of publication, typical number of citations per article, average length of article, etc.) that prevents it from being useful in comparing metrics across disciplines.
- Interdisciplinary journals are not well represented in the JCR database.
- In many fields, the correlation between JIF and citation rates for a particular article is weak.
- Editorial policies can affect the JIF.
Inappropriate use cases:
- As a journal level metric, the JIF should not be used as an indicator for the quality or impact of particular articles or authors.
- The JIF should not be used as an estimate of attention, discussion, or scholarly impact. Citations do not reflect all scholarly uses of the literature.
- The JIF is not statistically representative of individual journal articles. Due to the skewed distribution of citations (relatively few articles receive most citations, otherwise known as the long tail), the use of the mean rather than the median value of citations per article is misleading. The type of article can have significant impact on the number of resulting citations. For example, review articles are more frequently cited than other types of articles.
Available metric sources: Thomson Reuters Journal Citation Reports
Transparency: The process of selecting journals and article types for inclusion in the Journal Citation Reports database is not publicly documented, though the formula for calculating the JIF is public.
Timeframe: The JCR is typically released two years after the year in question. For example, the JIF for 2015 were released in 2017.