What the Journal Impact Factor Is
The Journal Impact Factor (JIF) is an annual citation metric for academic journals, calculated by Clarivate and published in the Journal Citation Reports (JCR). It descends from citation indexes created by Eugene Garfield in the 1960s–70s, originally to help librarians choose journal subscriptions.
A journal’s Impact Factor is the average number of citations received in one year by articles the journal published in the previous two years.
What the Journal Impact Factor Ranks
The JIF ranks academic journals within subject categories — producing ordered lists and quartiles (Q1 through Q4) that function as a prestige hierarchy for scholarly publishing.
It applies only to journals indexed in Clarivate’s Web of Science core collection — thousands of journals, but far from all scholarly publishing.
Core Inputs Used by the Impact Factor
Exactly two quantities:
- Numerator — citations in the current JCR year to items the journal published in the prior two years
- Denominator — the number of “citable items” (articles and reviews) the journal published in those same two years
Clarivate also publishes variants: the 5-year Impact Factor (same logic, longer window) and the Journal Citation Indicator (a field-normalized measure).
How the Impact Factor Is Calculated (High-Level)
The formula is a simple ratio:
- Count all citations this year pointing to the journal’s content from the last two years.
- Divide by the number of citable items published in those two years.
- The result — say, 8.5 — reads as “the average recent article in this journal was cited 8.5 times this year.”
Journals are then ranked within their subject categories and assigned to quartiles.
Conceptual model: A batting average for journals — citations per recent article, recalculated annually.
Update Frequency
The Journal Citation Reports, containing the new Impact Factors, are published annually, typically mid-year, covering the previous year’s citation data.
Known Limitations and Criticisms
- Skewed distributions — a small share of articles earns most citations, so the mean badly describes a “typical” paper
- Field dependence — citation rates differ by orders of magnitude across disciplines, making cross-field comparison meaningless
- Editorial gaming — coerced citations, self-citation, and “citation stacking” agreements between journals have led to JIF suppressions
- Misapplication to individuals — the JIF measures journals, not papers or people; using it to evaluate researchers is the central abuse targeted by the DORA declaration (2013)
- Two-year window — fast-moving fields are favored; fields with slow citation half-lives are penalized
Where the Impact Factor Is Used
The JIF is used for:
- Library subscription and collection decisions (its original purpose)
- Authors choosing where to submit manuscripts
- Tenure, promotion, and funding decisions — controversially, as a proxy for research quality
- Journal marketing (“Q1 journal” as a selling point)
Summary
The Journal Impact Factor is a two-year citation average that escaped its original context: built to rank journals for librarians, it became the default proxy for the quality of individual papers, researchers, and departments. Most of its criticism reduces to that category error — the metric itself is simple arithmetic; the misuse is institutional.
References and Sources
- Clarivate. Journal Citation Reports — Methodology (official documentation).
- Garfield, E. — founding papers on citation indexing.
- San Francisco Declaration on Research Assessment (DORA), 2013.
- Wikipedia. Impact factor.