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Journal metrics use citation data to rank and compare scholarly journals. Citation analyses are based on the premise that number of citations is an indication of the importance of a journal.
The status of a journal is commonly determined by two factors:
1. Popularity (e.g. number of citations a journal receives)
2. Prestige (e.g. sources of a journal’s citations)
The journal impact factor (JIF) is a statistical measure used to rank and evaluate journals and calculated by Thomson Reuters Web of Science database. Journal impact factors can be useful in deciding where to publish to improve the impact of you research output. Find out more about the journal impact factor score and journal citation reports (JCR) here.
Scopus (Elsevier) journal metrics are calculated using the Scopus database which covers more than 24,000 journals.
- SJR (SCImago Journal Rank) – measures the scientific prestige of a scholarly journal by assigning a relative score based on a citation network
- SNIP (Source Normalized Impact per Paper) – measures contextual citation impact by weighting citations based on the total number of citations in a subject field
- IPP (Impact Per Publication) is the average number of citations received in a particular year by papers published in the journal during the three preceding years.
- Individual articles should never be judged solely on the Impact Factor or other metrics for the journal in which an article is published.
- All journals have a spread of citations, and even the best journals have some articles that are never cited.
- Citation counts alone do not indicate the quality of the citations or the publication e.g. a work may be highly cited because it is controversial; this can distort the impact factor of a journal.
- Analyses are limited to the journals listed in the database you are using, e.g. JCR results are limited to the journals in the Thomson Reuters database, explaining why many journals do not have an Impact Factor.
- JCR calculations are based on a 2 or 5 year citation window compared with 3 years for Scopus calculations. A shorter citation window favours rapidly moving fields whereas a longer citation windows favours fields which build citations more slowly.
- Citations may be biased e.g. English language and review journals tend to be cited more frequently than works in other languages; authors may frequently cite their own work or the work of their colleagues.
- Review journals tend to have higher impact factors than original research journals in the same field because they tend to be cited more frequently.
- Only research articles, technical notes and reviews are “citable” items. Editorials, letters, news items and meeting abstracts are “non-citable items” and so do not contribute to Impact Factors and other metrics calculated from citation data.