Impact Factor Month

It’s Impact Factor month!

The Clarivate Analytics (formerly Thomson Reuters) Impact Factor (IF) is considered an established measurement of quality for the evaluation of journals. It is commonly used as a stand-in for the relative importance of a journal in any given field. But what is the history behind it? This month, we here at MDPI will be delving into the topics of Impact Factors and CiteScore to give you information that can help in your decision-making.

A brief history of Impact Factor

Born in 1925 and died in 2017, Eugene Garfield received his Bachelor of Science in chemistry in 1949. He then received his degree in library science in 1953 and a PhD in 1961. The idea of an impact factor came from his fascination with the idea of finding relevant journals. In 1955, he published his landmark paper in Science magazine. Five years later, the experimental Genetics Citation Index project began, leading to the publication of the 1961 Science Citation Index® (SCI®). Clarivate Analytics citation indexes used computer-compiled statistical reports, not only on the output of journals, but also in terms of citation frequency, laying the groundwork for what we know today as “Impact Factor”.

After using journal statistical data in-house to compile the Science Citation Index, Clarivate Analytics began to publish Journal Citation Reports® (JCR®). The JCR provides quantitative tools for ranking, evaluating, categorizing, and comparing journals. IF is one of these.

Impact Factor, however, has not been without criticism. Some have said that it unfairly hinders science by creating bias. While there has been criticism, Impact Factor remains an important metric that is often used as a shorthand for “how good a journal is”. It is clear that publishing in a journal with an Impact Factor can have an impact on how your work is perceived.

How is an impact factor calculated?

A journal’s Impact Factor is calculated based on two elements: the numerator, which is the number of cites in the current year to any items published in the journal in the previous two years; and the denominator, the number of substantive articles (source items) published in the same two years:

For example,

IF 2021 = 2021 cites of articles published in 2019–2020 / number of articles published in 2019–2020.

Does Impact Factor matter?

This is a bit of a “yes” and “no” answer. A journal’s IF does not affect your results or the data itself. Remember that your own work speaks for itself. However, a journal with a higher Impact Factor may be more selective in terms of what papers it will accept. And this means that it might have more prestige than one with a lower IF score. Impact Factors don’t say anything about individual citation rates, they only deal with the averages. Don’t worry too much about whether or not a journal’s Impact Factor will affect your paper (because it won’t). It’s also important to understand that some fields of study don’t have journals that have high Impact Factors. A little bit of research can help you to determine what the landscape of Impact Factors in your field looks like.

An interview with MDPI’s Head of Indexing

Our own Jenny Knowles interviews Katherine Winkel, MDPI’s Head of Indexing. Katherine takes some time out of her busy day to explain the difference between Impact Factor and CiteScore. She also gives a brief overview of indexing and how journals are indexed. And gives us some useful information about the different databases that some of MDPI’s journals are indexed in. One of the many things that Katherine explains is that Impact Factors and CiteScores are similar, but come from different sources.

Some of the other topics covered in this interview are common misconceptions about indexing, where MDPI journals are indexed, and how people can access indexing databases.

MDPI Journals with impact factors

We are very pleased to note that, in 2020, MDPI added ten new journals to its list of journals with Impact Factors. Some of these journals are Gels, Fermentation and Buildings. In total, MDPI now has 85 journals with an Impact Factor! We also saw a 96% of our journals receive a higher Impact Factor than the year before. For a full list of all MDPI journals that have Impact Factors, we encourage you to visit the website. In further exciting news, almost 40% of these journals ranked in the top 25% of journals (in at least one category). We’re excitedly looking forward to the 2021 results.

Did you know that MDPI journals, on average, receive their first journal Impact Factor after only 7 years from the journal’s launch? We’re proud of such a feat, especially considering that MDPI is a relatively young publisher.

Many open books.

We are proud to join the many amazing journals who have earned Impact Factors. And we look forward to adding many more MDPI journals to this list.

Other journal rankings

The two most famous rankings are Impact Factor and CiteScore. But there are a range of other rankings that serve different, important purposes. Journals are ranked in a number of ways, and they all serve slightly different purposes. Here are the most relevant ones and some of what you need to know about them.


Originally used exclusively for rewarding academics. h-index has more recently been used to rank journals. For MDPI journals with h-indexes, click here.

SJR indicator

The SCImago Journal Rank (SJR) indicator is derived from the average number of citations from each year and over a period of three years.


Calculated from the number of citations of a specific topic, Source Normalized Impact per Paper (SNIP) provides a way to address any possible inconsistencies between fields.

Web of Science

WoS has four different ranking indexes: SCIE, SSCI, AHCI, and ESCI. SCIE, the Science Citation Index Expanded, is probably the most notable one. SCI is dedicated to the best science and technology journals (and was established in 1964).

What about indexing databases and their associated rankings? We also explain PubMed and Medline, for example, along with others in a bit more detail in a comprehensive introduction to the subject.

Further reading

This month we are bringing you interviews and articles that deal with the subject as Impact Factors and CiteScores are released. This year, we hope to add many more journals to our list of journals with an Impact Factor. And we will share the news with you as we know more. As MDPI continues down the road towards being one of the best publishers of academic work in the world, Impact Factors are one of the many tools that will help get us there. If you want to see our current Impact Factor, we have that information readily available on our website!