Journal Impact Factors: What Are They

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Journal Impact Factors What Are They How Can
They Be Used?

• Pamela Sherwill, MLS, AHIP
• April 27, 2004

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History Of Impact Factors

• Created in the 60s to select journals for Science
  Citation Index
• Developed to compare journals regardless of their
  size
• Journal Impact Factors (IF) Article IF
• Size breadth of a scientific field determines
  super-cited papers
• Delays in reviewing and publication affects IF

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Impact FactorA Definition

• Journals with high IF publish articles that are
  cited more often than journals with lower IF. If
  citation numbers are taken as a measure of
  quality, then these journals are high ranking by
  this measure.

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Key Determinants

• The key determinants are not the number of
  authors or articles in the field but the citation
  density and the age of the literature cited. The
  average number of citations per article and the
  immediacy of citation are the significant
  elements. The size of a field will generally
  increase the number of super-cited papers.
• ---Eugene Garfield

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What Is An Impact Factor ?

• of current citations a journal receives divided
  by the number of articles published in the two
  preceding years
• Citation Half Life
• How long articles in a journal continue to be
  cited after publication

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Citation Density

• Mean of references cited per article
• Varies by discipline lower in math than life
  sciences
• Higher in review articles
• Half-Life
• of retrospective years required to find 50 of
  the cited references

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Calculating Impact Factors
of citations in the current year for a journal
items published in the journal for the last 2
years
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What Influences IF?

• Review articles cited more often
• Case reports rarely cited
• Rapid publication time gt
• Self-citations gt
• Bias towards rapidly evolving fields
• Cites not counted after 2 years
• Specialty journals have lt IF

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Impact Factors

• Scientific journals score gt than clinical ones
• US journals score gt than European
• Review articles score gt than original articles
• Methodological papers may score gt than those with
  new data
• Free electronic access gt the IF of a journal

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How Are IFs Used?

• Judge a publications quality or prestige
• Assess academic productivity
• Authors choosing where to publish
• Evaluate an author or journal editor
• Decisions for tenure promotion
• By libraries to make collection decisions

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Nursing Journal Facts

• Journal Citation Reports (the source of IFs)
  rates 33 general nursing journals
• PubMed indexes 248 refereed nursing journals
• CINAHL indexes 548 active nursing journals
• ISI regards librarians as their primary customers
• ISI to gt of Nursing journals by 23 in 2006

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Determining Journal Quality

• Nursing limited of journals rated (33)
• General nursing journals not specialty
• Nursing journals impact factors lt2
• IF does not measure impact of specific articles
• Not every article in a high impact journal is of
  high quality

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Self-Citations

• Encouraged by some editors/journals
• Not subtracted when IF is calculated
• Authors accumulate many self-citations
• ISI claims it has little effect on the relative
  rank of highly ranked journals
• Journals with IF lt .5 have high self- citation
  rates

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Issues With JCR Database

• Prestige/quality is a murky concept
• Recent articles not enough time to be cited
• Citations not evenly distributed among articles
  in an issue
• Journal impact factor not article impact factor
• Pure clinicians read clinical articles but do not
  write or cite

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Issues With JCR Database(continued)

• Rapidly expanding fields tend to have gtIF
• Letters, editorials, and news items not counted
  in article total but if cited are counted as
  citations for the journal
• Small of articles lead to a large proportion of
  citations in a journal
• Limited of evaluated journals

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Impact Factor Limitations

• Reflect the journal rather than the article
• Vary with time in numbers ranking
• Changes in clinical interest affects IF
• Not related to the peer review process
• Can be manipulated by authors or editors
• 2-year period is arbitrary - not empirically
  based
• Journal availability affects the ranking
• Author citation errors

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Limitations (continued)

• Journal IF involve large populations of articles
  and citations
• Authors produce smaller numbers of articles
• 80/20 rule 20 of the articles account for 80
  of the citations
• IF can vary from journal issue to issue
• IF vary from year to year
• Lack of empiric studies on IF as measure of
  quality

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Impact Factor Alternatives

• No other formal evaluation tool
• Professional recommendations
• Refereed journals
• Editors reputation
• Editorial standards
• Experience stature of editor board

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Alternatives

• Time from acceptance to publication
• Acceptance/rejection rate
• Best quality journals are often most competitive
  in acceptance for publication

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Thank You