06 Frequently asked questions
Download our current full list of FAQs (PDF)
How can I access the metrics?
Both metrics are freely available on the www.journalmetrics.com. SJR is also available on the SCImago Journal and Country Ranking website.
My institution has been using the Journal Impact Factor (JIF) to evaluate journals for many years. Why should we consider SNIP & SJR?
The changing parameters of journal publishing, as well as constantly changing subject fields and cross-discipline citation demand more detailed tools that can account for these changes.
How does SNIP & SJR compare to the JIF?
SNIP & SJR are two of the metrics that have been added to the general toolbox of journal evaluation tools. They are simply a new perspective on citation behavior.
Where do SNIP & SJR gather source data?
All SNIP & SJR citation information is gathered using Scopus, the largest scientific abstract and citation database. Both metrics will be applied to all Scopus peer-reviewed content – nearly 18,000 journals, proceedings and book series.
Why a three-year citation window?
Evaluating citations over a period of three years ensures that the majority of journals have reached their citation peaks. Studies show that three years is the most appropriate time frame to consider.
Which tool should I use?
To compare journal citation behavior with other journals, whether in- or outside your journal’s subject field, SNIP is the most accurate and balanced metric available. To measure the value of citations based on journal prestige and influence, SJR is the tool you need.
When will new metric values be published?
We will update twice per year.
In 2010, the second update will be in September, and a 2010 metric will be available.
From 2011, we will update in April and September. In April the first version of that year’s metric will be available – so in April 2011 there will be a 2011 metric.
The prestige that a journal transfers when it cites another journal is equal to its SJR for that year, and yet citing is used to generate the SJR. This seems very circular – how does it work?
The process does seem circular, and it’s certainly not easy to understand how one thing that is not calculated yet can be used to calculate the ranking for other journals. But it is possible by using an iterative process which is what we are using here.
The iterative process runs until the differences between prestige values of journals in two consecutive iterations is not significant. When this steady-state is reached, whatever values the journals have are their SJRs for that year.
- To start off the process, you have to assign an arbitrary value to all the sources in the database – you cannot start things off when all sources are valued as 0.
- It could be anything, but SCImago sets this arbitrary value at 0.1, meaning that every source inside Scopus starts with an SJR of 0.1
- All sources outside Scopus (not indexed) have a value of 0.
- 0.1 therefore represents a minimum prestige that every journal achieves just by being included in the database.
- In the first round of the iterative process, all citations are worth the same because all the journals have the same prestige.
- The first round will just calculate raw impact – average citations per document. But because this value is different for each source (think of the Impact Factor – it is similar), each journal will have a different first round value.
- You can’t stop here because the real aim of SJR has not been applied yet – not we have to start to distinguish between the value of the citations depending on the prestige of the journal that they come from. To apply the prestige factor, we need to run more rounds.
- The first round average citations per document value acts as the journal’s prestige for the second round.
- In this second round, citations have different weight depending on the journal they come from, and this will change the values assigned to other journals they are citing.
- Values at the end of this round will be different from those at the end of the first round.
- We keep repeating step 3 until the steady-state is reached.
SCImago have submitted an article with details of the calculation method.
