As announced in March, we have several enhancements coming in the 2023 Journal Citation Reports (JCR)™ release. One change is that we will display the Journal Impact Factor (JIF)™ to one decimal place, rather than the current three decimal places, to encourage users to consider other indicators and descriptive data in the JCR when comparing journals. By reducing the decimal places from three (X.000) to one (X.0), we will see an increase of rank position ties in many categories – i.e., multiple journals with the same JIF.
These changes will only impact the 2022 metrics, to be released in June 2023, and will not impact earlier JIFs, rank and quartiles.
JIF ties are not new to the JCR, but they are infrequent when using three decimal places. With the move to one decimal, ties will be more common, so we want to set out clearly how JIF ties work when calculating subject category rank and quartile. Rankings for ties can be handled in different ways but the longstanding approach for JCR is to assign journals with the same JIF in the same category with the same rank position, skipping the ranking position or positions for the journal with the next lower JIF value. This is commonly known as sparse ranking.
Example – Title C and D have the same 1.5 JIF and rank of 3. The next title, Title E, is rank 5 where the 4th rank position is skipped.
While a journal has a single JIF, it can be assigned to multiple categories. A journal is assigned a JIF rank and quartile for each category assigned. If a journal is in two categories, it will have two ranks and quartiles, one for each category.
Quartiles are calculated based on the rank position within a given category, specifically using a longstanding value we refer to as ’Z’. Z is calculated by dividing a journal’s rank position in a category by the number of journals in that category. The quartile is determined by where Z falls in the scale of 0.0 – 1.0 (see chart). Since journals with a shared JIF in the same category share the same rank position, they also share the same quartile.
Using the same example for ties, we calculate the quartiles with the Z values determined by rank position. Titles C and D share the same JIF, the same rank position and the same quartile.
Quartile distribution changes: move to JIF with one decimal
The move to one decimal place from the current three will create some changes in the quartile distribution, as discussed in the earlier blog. The exact change in quartile distribution will depend on the category. Some categories will see little to no change in quartile distribution, particularly if there are no JIF ties. Categories with more ties and a low range between the highest JIF and lowest JIF will see more quartile distribution changes.
Using sample data from the 2021 metrics, we analyzed two categories to provide examples of how the quartile distribution may change with the move to one decimal point. The below are for illustrative purposes only and do not represent the actual changes that will be seen with the June 2023 release.
Example: minor quartile change (2021 JCR Data)
Entomology is a category illustrating minor quartile changes. It is a larger than average category with a wide range of JIF values between the highest and lowest, 22.7 (highest) – 0.2 (lowest). The number of ties increased from four tied journals with 98 distinct rank positions to 83 tied journals with 42 distinct rank positions. Even with this increase in ties, the quartile distribution changes only slightly. Two quartiles see a change of +/- 1 journal and two quartiles are entirely unchanged.
Example: major quartile changes (2021 JCR Data)
We see a more significant change in quartile distribution for the History category. History is a smaller category with a smaller range of JIF values, 4.9 (highest) – 0.2 (lowest). This reflects different citations patterns compared to Entomology above. JIF ties in the History category increased from none with 48 distinct rank positions to 31 journal ties with 27 distinct rank positions. All four quartiles are impacted, with two additional journals in Q1 and Q3, and two fewer journals in Q2 and Q4. Note that ties can occur with more than two journals.
The key points to remember are:
- Journals with tied JIFs will always share the same rank and quartile in a category.
- The number of ties seen in the JCR will increase as we move from three decimals to one decimal.
- Quartile distribution shifts will vary between categories depending on the category characteristics.
We encourage you to consider other indicators and descriptive data in the JCR when comparing journals, such as the Journal Citation Indicator – a normalized journal-level metric that can be easily interpreted and compared across disciplines.
This is the second in a series of updates and analyses of how the expansion of the JIF to more quality journals will translate to changes in rankings and quartiles in JCR and explain how users can use JCR filters to view rankings that only include journals from editions of interest. Bookmark this page and stay tuned for further updates.