Tools to measure journal impact
In which journal should you publish your own research? You can look at the scope of the journal, the visibility of the journal, the time between the acceptance and the publication of an article. You can also take into account the journal performance in terms of the number of citations received.
Several journal-level metrics are available. The most well-known is the Journal Impact Factor (JIF) from Thomson Reuters. Scopus (from Elsevier) also offers journal-level metrics, including the Source Normalized Impact per Paper (SNIP), the SCImago Journal Rank (SJR) and CiteScore.
You can read more about the journal-level metrics in the course Research Impacts: sources and metrics.
Use journal-level metrics with care!
The San Francisco Declaration on Research Assessment (DORA), signed among others by the VSNU, the Association of Universities in the Netherlands, recommends not to 'use journal-based metrics, such as Journal Impact Factors, as a surrogate measure of the quality of individual research articles, to assess an individual scientist’s contributions, or in hiring, promotion, or funding decisions'. When you do use journal-level metrics, be aware that …
- Many journals do not have an impact factor.
- It is possible that an individual article published in a journal with a high impact factor is never cited. So the impact factor of the journal says nothing about the quality of individual articles within that journal.
- The impact factor of a journal can be distorted by just one article receiving a lot of citations (for example a controversial paper).
- The citation patterns differ greatly between research fields. An Journal Impact Factor of 2 can be high in one field and considered low in others. This means you can't compare them directly. Look at rankings within the fields or look at normalized indicators.
- In the calculation of the impact factor a citation window is used (for example two or three years). In some fields citations are given to older articles.
- Citation bias may exist: English language resources may be favored.
- In general, reviews receive more citations than articles (with original research). Journals with a large proportion of reviews will have a higher impact factor.
- Definition: Average number of times articles from a journal published in the past two years have been cited in the JCR year.
For example: The 2014 Journal Impact Factor of the journal Appetite is 2.291: this means that the articles published in 2012 and 2013 have been cited in 2014 on average 2.291 times.
- Available in the Journal Citation Reports, published by Thomson Reuters. In the JCR you can find impact factors for over 11.000 journals. The JIF is published once a year (normally in June).
- The citation data is based on Journal Citation Reports data.
- In the JCR you can also get the JIF without journal self cites and the 5 year Impact Factor – taking into account the citations to articles published in the five previous years.
To compare journals you can’t just look at the JIF: the citation patterns differ greatly between research fields. JCR also shows the rank of a journal within its categories, the Quartile and the JIF Percentile. This makes comparison between different fields possible.
For example the journal Appetite is in 2014 ranked as 23 of 51 journals, within the category Behavioral Sciences. This means the journal is in Q2, the second Quartile. The JIF Percentile is 55.882 – 55.882 percent of the journals in this category have a lower Journal Impact Factor.
- Description: the Eigenfactor Score is a ‘measure of the journal's total importance to the scientific community’. The calculation is based on the number of times articles from the journal published in the past five years have been cited in the JCR year, but it also considers which journals have contributed these citations so that highly cited journals will influence the network more than lesser cited journals. References from one article in a journal to another article from the same journal are removed, so that Eigenfactor Scores are not influenced by journal self-citation.
An Eigenfactor score of 2 means that the journal has twice as much total influence as the average journal in the JCR.
- Available in Journal Citation Reports (from 2007) and via www.eigenfactor.org (from 1997).
Eigenfactor also publishes the Article Influence Score (also available in JCR): the average influence of a journal's articles over the first five years after publication.
- Description: SNIP measures the average citation impact of the publications of a journal, calculated as the number of citations given in the present year to publications in the past three years divided by the total number of publications in the past three years. SNIP citations are normalized in order to correct for differences in citation practices between scientific fields. Essentially, the longer the reference list of a citing publication, the lower the value of a citation originating from that publication.
- The citation data is retrieved from Scopus.
- Available in Scopus (under Sources), CWTS Journal Indicators (from 1999) and Journal Metrics (from 2011).
- Description: the average number of weighted citations received in the selected year by the documents published in the selected journal in the three previous years. SJR is weighted by the prestige of a journal. Subject field, quality and reputation of the journal have a direct effect on the value of a citation. SJR also normalizes for differences in citation behavior between subject fields.
- The citation data is retrieved from Scopus.
- Available in Scopus (under Sources), SCImago Journal & Country Rank (from 1999) and Journal Metrics (from 2011).