The Journal Impact Factor should be used with careful attention to the many phenomena that influence citation rates both at the article level and at the journal level. For example, the subject area and subtopic, the communications goal of a particular journal and how that affects the type of materials published, the dynamics and needs of the authors and the community that participate in the journal, and other simple bibliometric features of the article, journal, and topic. Journals that consistently have a high Journal Impact Factor are consistently publishing materials that are cited in the scholarly literature two and three years later, but there is no direct relationship between the JIF and the current or expected citation count of any specific article. When the Journal Impact Factor is used with informed peer review, it is possible to make more meaningful assessments of the dynamic relationship between article performance and journal performance. No journal metric can be used as a proxy for article or author impact; therefore, JIF can only be considered as one of many factors in the assessment of performance. The full visibility of article-level contribution to JIF provides a clearer understanding of the reciprocal relationship between the article and the journal. The inclusion of the Journal Citation Indicator (JCI), a metric that is normalized to account for some of the factors that influence citation activity supports a more robust, cross-topical consideration of impact.
You should also consider the following four conditions, which may affect journal's ranking and Impact Factor.
Impact Factor by Article Type
Clarivate manually codes each published. item with a document type, but it is not feasible to individually code the millions of references processed each year. The Citation Distribution graph will show the relative citation profile of articles, reviews, and all other, non-citable document types, allowing you to visualize how each of these types influence the JIF. Unlinked citations are reported here as well. These citations were not successfully linked to individual published items, so the type of document cited is unclear. Using the Journal Impact Factor Contributing Items data, you can export all the articles and reviews, and their individual citation contribution to the JIF. This allows a detailed analysis of citation impact at the item, topic, and type level. Significant changes in the published materials in a journal can lead to short-term changes in overall citation impact.
Changes in Journal Format
Sudden changes in a journal's size can affect the JIF. The average number of cites per article is lowered when there are more one-year-old articles than two-year-old articles included in the JIF calculation because article citation rates tend to increase in the second year after publication. Similarly, when an article counts drops, the JIF may rise temporarily. The item counts and list of specific items in the JIF are provided, so that any sudden changes can be noted.
Title Changes and Citation Metrics
After a title change, two JCR years must pass before the new title fully replaces the previous title in JCR. In the first year after a journal title change, the new title is listed with an Immediacy Index but no impact factor because the article counts for the two preceding years, used in Impact Factor calculations, is zero. The superseded title is listed with a normal two-year JIF. One year later, JCR lists separate impact factors for the new title and for the superseded title, but only the new title will have an Immediacy Index. In this second year, the JIF for a new title may be lower than expected because the article count includes only earlier articles. Similarly, the JIF for the superseded title may be higher than expected because it is based upon only older articles. To calculate a unified JIF, you can total the cites to the two previous years and divide that by the sum of the article counts for the two titles.
Cited-only Journals in JCR
Some of the journals listed in JCR are not citing journals but are cited-only journals. A journal that has no Citing Journal page information is a cited-only journal. Cited-only journals were not indexed as source items. They may represent former titles, titles that have been removed from coverage, or titles that are not selected for coverage in Clarivate’s citation databases.
This is significant when comparing journals because self-citations from cited-only journals are not included in the JCR data. Self-citations represent a significant percent of the citations that a journal receives. Evaluations including cited-only journals are enhanced by self-citation analysis