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The h-index is the highest number x so that x articles by a given journal or author have been cited at least x times. For example, if a journal has an h-index of 100, it means it has 100 articles that have been cited at least 100 times.
While h-index is often used to assess the performance of individual authors, it can also be applied to journals. This metric looks to assess both volume of production and impact. It seeks to promote meaningful publication.
For its metrics, Google Scholar uses the h5-index. This is a variation of the h-index where the same formula is applied to the period spanning the five previous complete years. To learn more about metrics provided in Google Scholar, go to the "Additional Sources of Journal Metrics" section of this guide.
This metric is mostly used to assess the publication output of individual authors. The g-index will be the highest number x so that the x most cited papers by an author, taken together, have at least x² citations. For example, a g-index of 10 means that an individual’s 10 most cited papers, taken together, have received at least 100 citations.
SNIP is a metric developed by Elsevier that takes into account how often citations occur in specific disciplines. There are some disciplines where papers tend to have a very high number of references compared to papers in other areas of study. This is because publication patterns and scholarly communication practices differ from one field to the next, sometimes very significantly. SNIP takes into account these differences by assigning greater weight to citations that occur in disciplines where they are less frequent.
This metric could prove very useful if you are comparing two journals that fit in the same broad subject category but that specialize in two different subdisciplines within that subject category. Even within the same general subject area, citation practices can vary widely between subdisciplines. It is therefore possible that if you compare these two journals, even if they are similar in quality, you will see huge differences in metrics that are based on raw citation counts, such as CiteScore or Journal Impact Factor. This can be misleading. SNIP is designed to correct for these differences in citation practices when measuring journal impact.
To learn more about SNIP, you can click here. This link will take you to a page that gives the SNIP score for the Journal of Environmental Sciences. Scroll down to a section of the page titled "Definition". There you will find a full explanation of SNIP and how it is calculated.
Eigenfactor seeks to measure the influence of a given journal in comparison to all the other publications that make up the scholarly publishing landscape. This metric is based on the publications included in the Journal Citation Reports (JCR). Eigenfactor takes into account the citations received by a particular journal, but weighs these citations differently according to the influence of the citing publication. Citations appearing in highly influential journals will have a greater positive impact on the Eigenfactor of the cited publication.
It is important to know how to interpret the Eigenfactor score. In the Eigenfactor formula, the journals included in JCR, all taken together, are assigned a score of 100. The Eigenfactor score of a specific journal signifies its portion of that total score of 100. It therefore reflects how much influence that specific journal has within the entire landscape of considered publications. So if a journal receives an Eigenfactor score of 1.5, this means that according to the Eigenfactor method, that journal has 1.5% of the total influence within the whole scholarly publishing landscape.
You can find a couple of additional metrics in www.eigenfactor.org. These are briefly described below:
To learn more about the Eigenfactor Project and its metrics, click here.
The following links provide more information about various journal metrics.