What is a good impact factor for a journal?

There is no universal threshold for a 'good' impact factor, as it varies widely by field. In many disciplines, an impact factor above 10 is considered excellent, while in others, a score above 2 may be very strong.

How is the impact factor calculated?

The impact factor is calculated by dividing the number of citations in the current year to articles published in the previous two years by the total number of citable articles published in those two years. It is published annually in Journal Citation Reports.

Can impact factor be manipulated?

Yes, impact factor can be manipulated through practices like excessive self-citation, citation stacking, or publishing more review articles, which tend to be cited more frequently. These tactics undermine the metric's reliability.

Is impact factor the same as CiteScore?

No, impact factor and CiteScore are different metrics. CiteScore calculates citations over four years instead of two and includes a broader range of document types, while impact factor uses a two-year window and only counts citable items.

Why is impact factor criticized?

Impact factor is criticized for being easily skewed by a few highly cited papers, not representing individual article quality, and varying greatly across disciplines. It also does not account for the quality of citations or open access availability.

What Is Impact Factor? A Simple Guide for Researchers

If you have submitted a manuscript to an academic journal, you have likely seen the term “impact factor” listed on the journal’s homepage or in its promotional materials. In simple terms, the impact factor is a number that reflects how often the average article in that journal has been cited in a given year. It is a metric used to compare journals within a field, and it often influences where researchers choose to submit their work.

How the Impact Factor Is Calculated

The impact factor is calculated by Clarivate, the company that owns the Web of Science database. It is a three-year snapshot.

The formula is straightforward. For a given year, the impact factor equals the number of citations received in that year to articles published in the previous two years, divided by the total number of “citable items” published in those same two years. Citable items are typically research articles and reviews, not editorials, letters, or news pieces.

For example, to calculate the 2023 impact factor for a journal, you would take all citations in 2023 to articles the journal published in 2021 and 2022. You then divide that number by the total number of citable articles published in 2021 and 2022. The result is a single number, usually expressed to one decimal place. A journal with an impact factor of 5.0 means that, on average, each article published in the previous two years was cited five times in the calculation year.

What Counts as a Citation?

A citation is counted when a new article in a Web of Science-indexed journal references a previous article. Self-citations are included, though Clarivate applies some checks to prevent journals from artificially inflating their score through excessive self-citation. Citations from books, conference proceedings, or non-indexed journals are not included in the calculation.

What the Number Actually Tells You

The impact factor is often misunderstood. A high impact factor does not mean a journal is of higher “quality” in any absolute sense. It simply means that its articles, on average, are cited more frequently within a short window of time. This is a measure of visibility and immediate influence within the academic community.

Here is what the impact factor is useful for:

Comparing journals within the same discipline. A journal with an impact factor of 3.0 is likely more widely read and cited than a journal with an impact factor of 1.0 in the same field.
Identifying leading journals. Many top-tier journals in fields like cell biology or general medicine have impact factors above 10.
Making initial submission decisions. Researchers often aim for journals with higher impact factors to maximize the reach of their work.

Important Limitations

The impact factor has several well-known problems.

It is not a measure of individual article quality. A journal with a high impact factor may still publish many articles that receive few citations. The metric is an average, and a single highly cited paper can skew the entire number.
It varies dramatically by field. Journals in mathematics or engineering often have much lower impact factors than journals in molecular biology or clinical medicine. Comparing a math journal to a cancer research journal is meaningless.
The time window is short. The two-year window favors fast-moving fields where research is cited quickly. In fields like history or sociology, where citations may accumulate over many years, the impact factor underrepresents a journal’s true influence.
It can be gamed. Some journals have used strategies like publishing large numbers of review articles or coercing authors to add citations to the journal in their reference lists. Clarivate has delisted journals for such practices.

Alternatives and Complementary Metrics

Because of the limitations, other metrics have been developed.

The Journal Citation Indicator (JCI)

Clarivate introduced the Journal Citation Indicator in 2021. It normalizes the citation impact of a journal by field, so a JCI of 1.0 means the journal is at the average for its field. This makes cross-field comparison more fair than using the raw impact factor.

Scopus CiteScore

Elsevier’s Scopus database offers CiteScore, which uses a four-year citation window and includes all document types. It is calculated over a broader range of journals than the Web of Science.

Eigenfactor and Article Influence Score

The Eigenfactor score considers not just the number of citations but also the source of those citations. A citation from a highly influential journal counts more than one from a lower-tier journal. The Article Influence Score is a normalized version of this metric.

How to Use Impact Factor Responsibly

If you are a researcher deciding where to submit your next paper, the impact factor is one data point among many. It should not be the only factor. Consider these questions as well:

Does the journal’s scope match your paper? A paper on a niche topic may be rejected from a high-impact general journal, wasting months.
What is the journal’s acceptance rate? High-impact journals often have acceptance rates below 10 percent.
Is the journal indexed in the databases your colleagues use? A journal with a moderate impact factor that is widely read in your specific subfield may be more valuable than a high-impact journal that few in your area follow.
What is the review timeline? Some high-impact journals are very slow. For time-sensitive research, a faster journal with a slightly lower impact factor may be preferable.

For evaluating a journal’s reputation, you can also look at the editorial board, read a few recent articles, and ask colleagues in your network. No single number captures the full picture of a journal’s value or the quality of the research it publishes.

Key Takeaways

The impact factor is a journal-level metric that measures the average number of citations per citable article over a two-year window.
It is calculated by Clarivate using data from the Web of Science and is most useful for comparing journals within the same discipline.
The metric has significant limitations: it does not reflect individual article quality, it varies by field, and it can be manipulated.
Alternative metrics like the Journal Citation Indicator, CiteScore, and Eigenfactor provide additional perspectives on journal influence.
Use the impact factor as one piece of information when choosing a journal, but prioritize fit, audience, and editorial standards.