Bibliometric measures

Journal metrics are used to evaluate the visibility of a journal total output, and provide indication of the quality control measures, in terms of peer review process, transparency of practices, ethical standards and other criteria. Journal level metrics should not be used to judge the impact of an individual article or author.

The most common used measures are:

• Journal Impact Factor: this is a measure of the frequency with which the average article in a journal has been cited in a particular year period. It is calculated as all citations to the journal in the current year to items published in the previous two years, divided by the total number of scholarly items (these comprise articles, reviews, and proceedings papers) published in the journal in the previous two years.
• 5 year Journal impact factor: this is the average number of times articles from the journal published in the past five years have been cited in the year of interest. It is calculated in the same way as the Journal Impact Factor but with on a five year window.
• Journal citation indicator: this is a field-normalized index designed to complement the Journal Impact Factor, with the intent to compare journals across different disciplines.
• Scimago Journal Rank: this expresses the average number of weighted citations received in the selected year by the documents published in the selected journal in the three previous years. A weighted citation assigns a higher score to publications in prestigious journals than those from a title that has a smaller citation network.
• Journal acceptance rate: this is the percentage of submitted manuscripts accepted for publications in a journal.

Article-level metrics provide information of how an article is being discussed and used.

These includes

• Citation count: the total number of times an article has been cited by other research articles.
• Mentions on media: number of times an article appears on social media, news, blogs, or other media type resources.
• Views: the number of views and/or downloads of an article from a publisher website, repository, or online platform.
• Saves: number of times the article has been saved on Mendeley Library by Mendeley users.

These metrics are usually provided by the journal where the article is published, or by the repository where the article is deposited.

It is important to evaluate the citation of an article in the right context; for example, citations need time (at least two years!) to build up and this vary according to the discipline. For new articles the mentions on media may be more relevant as they indicate the attention that an article is receiving before academic citations accrue.

Author metrics indicate the citations for a given author.

The most common used indexes are:

• h-index: measures the cumulative impact of a researcher's output by looking at the number of citations a work has received – a h-index of value=h indicates that the author has h number of publications that have been citated at least h times.
• i10-index: created by Google Scholar, it measures the number of publications with at least 10 citations.
• g-index: aims to improve on the h-index by giving more weight to highly-cited articles.

However, these indexes can be misleading if used out of context and should never be used to directly compare individuals because (see also the UoA responsible metrics policy for more information):

• The  h-index and i10-index do not consider highly cited papers.
• All indexes can change drastically from a year to another.
• The number of papers and citations differs dramatically among fields and at different points in a career.
• Author's index values are predominantly driven by the oldest papers, which have had more time to accrue citations. Recent papers – which may be more relevant or of higher impact – have little to no effect on the score.
• The index values vary according to the metric source used: for example, Web of Science and Scopus tend to assign lower h-indexes than Google Scholar.

Altmetrics are complementary metrics that work alongside traditional metrics to produce a comprehensive picture of how research is being received around the world. Research visibility is measured through mentions count on social media, blogs, policies, news sites and other web media in the attempt to evaluate the attention surrounding an article, a researcher, a journal, or an institution.