Understanding Impact Factors

By Lesley Granberg posted 08-28-2023 02:31 PM

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Imagine you are approaching the fifth year of your Ph.D. program. Your PI tells you that in order to graduate you need to ensure you have at least one first author publication. Basic knowledge about impact factors for journals tells us that the higher the number the better the journal, right? In 2023 there is more to the story, and I would like to debunk the myth of the infamous impact factor by spending some time describing what they are and what they are not.

The impact factor was originally established by Eugene Garfield, the founder of the Institute for Scientific Information (1). The concept of an impact factor or IF is a measure that reflects the number of citations a certain journal article has received across a variety of media types. They are calculated once a journal has completed a minimum of three years of publication, making it impossible to calculate the IF for newer journals. For example, the impact factor calculated for our journal SLAS Discovery is noted to be 3.1, and was calculated using the formula seen below:

This calculation was recently updated in 2022, where instead of using the year of publication of an issue to determine the publication date of an article, Clarivate (the company which calculates the impact factor using data from the Web of Science) now uses the so-called “early access” (EA) date, or when the article first appears online. The EA is a version of record of the article that will not change but is not dependent on publication in an issue. Clarivate also uses services/applications such as Publons, EndNote, EndNote Click, and ScholarOne (2).

The impact factor, however, should not be the be-all and end-all when deciding where to publish your primary research. Another citation-based metric is the SCImago Journal Rank, or SJR Indicator, which not only considers the number of citations an article has received, but also incorporates how frequently is this journal cited by others (3). A journal with a SJR value > 1.0 has above average citation potential and journal with a SJR value < 1.0 has below average citation potential (3). The SJR for SLAS Discovery is 1.042, placing it slightly above the average citation potential.

Similarly, another metric is the Source Normalized Impact per Paper, or SNIP, which calculates the mean citation frequency of the articles in a journal by normalizing to the mean citation frequency of other articles in this field (4). The SNIP for SLAS Discovery is 0.632 (5) placing our journal slightly below 1, where a SNIP value of 1 means the journal is average in its field when considering citation rates (6).

Although SJR and SNIP are additional methods to help guide the decision-making process of which journal to publish in, they still miss some elements of impact from these calculations, such as the impact of social media, in particular. This is where the field of Altmetrics comes into play, a term I only learned about recently when researching for this blog. Altmetrics is a combination of the words alternative and metrics, and is specifically used to determine the role of social media and its influence on academic publications (6). This is becoming increasingly important as the open access online content from our journals is currently being accessed, used, and shared on websites and in videos, thus going beyond the traditional idea being cited in other peer-reviewed publications (7).

With these thoughts in mind, what other factors besides IF and some mentioned here do you think should be considered when looking for a home for a new publication?

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