impact factor (IF)

The impact factor (IF) or journal impact factor (JIF) of an academic journal is a scientometric index calculated by Clarivate that reflects the yearly mean number of citations of articles published in the last two years in a given journal, as indexed by Clarivate's Web of Science. As a journal-level metric, it is frequently used as a proxy for the relative importance of a journal within its field; journals with higher impact factor values are given the status of being more important, or carry more prestige in their respective fields, than those with lower values. While frequently used by universities and funding bodies to decide on promotion and research proposals, it has come under attack for distorting good scientific practices

Calculation

In any given year, the two-year journal impact factor is the ratio between the number of citations received in that year for publications in that journal that were published in the two preceding years and the total number of "citable items" published in that journal during the two preceding year

Cited Half Life

Many journals brag about publishing up-to-date, cutting edge research and most researchers want to publish their work in such journals. Journal cited half-life, also known as aggregate cited half-life, is a measure sometimes used to evaluate the current interest in a journal. However, journal cited half-life is not a reliable measure of this and should be used with care.

A journal may be cited hundreds or thousands of times per year but the articles cited will vary in age. Some will be only a few months old, having been published in the same calendar year as the citation; other articles may have been published decades before. Journal cited half-life counts all the journal citations during one calendar year and calculates the median article publication date—half of the cited articles were published before this time, half were published afterwards. The number is expressed as years before the calendar year of interest, e.g., for the year 2012, a cited half-life of 5 years means that half of all the cited articles were published before January 1, 2008 and half were published afterwards. The phrase “half-life” is an awful, misleading descriptor of the concept but is obviously thought to be catchier than “cited journal median publication year.”

H-index

The h-index, or Hirsch index, measures the impact of a particular scientist rather than a journal. "It is defined as the highest number of publications of a scientist that received h or more citations each while the other publications have not more than h citations each." 1 For example, a scholar with an h-index of 5 had published 5 papers, each of which has been cited by others at least 5 times. The links below will take you to other areas within this guide which explain how to find an author's h-index using specific platforms. 

NOTE: An individual's h-index may be very different in different databases. This is because the databases index different journals and cover different years. For instance, Scopus only considers work from 1996 or later, while the Web of Science calculates an h-index using all years that an institution has subscribed to. (So a Web of Science h-index might look different when searched through different institutions.) 

The following resources will calculate an h-index:

Scopus

Web of Science

Google Scholar

G-index

The g-index is calculated based on the distribution of citations received by a given researcher's publications, such that:

given a set of articles ranked in decreasing order of the number of citations that they received, the g-index is the unique largest number such that the top g articles received together at least g2 citations.

SNIP

Source-normalized Impact per Paper (SNIP) is a field normalised assessment of journal impact. SNIP scores are the ratio of a source's average citation count and 'citation potential'. Citation potential is measured as the number of citations that a journal would be expected to receive for its subject field. Essentially, the longer the reference list of a citing publication, the lower the value of a citation originating from that publication. SNIP therefore allows for direct comparison between fields of research with different publication and citation practices.

The Scopus database is the source of data used to calculate SNIP scores. SNIP is 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. A journal with a SNIP of 1.0 has the median (not mean) number of citations for journals in that field.

SJR

Scimago Journal Rank (SJR) is a measure of the prestige of scholarly journals. SJR scores are computed using network analysis of citations received by journals. The methodology accounts for number of citations as well as the source of citations, with citations from high prestige journals being worth more than those from journals with lower prestige. The prestige value depends on the field, quality and reputation of the source journals that citing article is published in.

By incorporating citation behaviour in different disciplines into account, SJR can be used to make comparisons between journals in different disciplines. The effect of SJR is to flatten differences between fields i.e. citations in high cite fields (e.g. neuroscience, pharmacology) are worth less than a citation in a low cite fields (mathematics, humanities).

SJR only considers peer reviewed articles, reviews and conference papers.

Scimago uses the Scopus database and journal classification scheme to rank journals by quartiles across subject areas. Computation of SJR is an iterative process that distributes prestige values among the journals until a steady-state solution is reached, similar to the methodology used for Google PageRankTM. The average SJR value for all journals in Scopus is 1.000.

SJR scores are available from the two databases listed below: SCIMago Journal and Country Rank and Scopus.

SCImago is a research group from the Consejo Superior de Investigaciones Científicas (CSIC), University of Granada, Extremadura, Carlos III (Madrid) and Alcalá de Henares, dedicated to information analysis, representation and retrieval by means of visualisation techniques.

CiteScore

CiteScore Currently available for over 22,000 journals indexed in Scopus, CiteScore aims to capture the optimum citation period for most subject areas. It is a ratio of citations to research published and looks at all content published in a journal (not just articles and reviews).

How it’s calculated: All citations recorded in Scopus in a given year to content published in the previous three years/The number of items published in a journal within the previous three years.

5 YEAR IMPACT FACTOR

The 5-Year Impact Factor attempts to reflect the longevity of research and is more stable yearon-year for smaller titles as there are a larger number of articles and citations included. These are useful for subject areas where it takes longer for work to be cited.

How it’s calculated: Number of citations in one year to content published in the previous five years/ Number of articles and reviews published within the previous five years.

Eigenfactor

The Eigenfactor measures the influence of a journal within the relevant literature over 5 years. A citation from a highly cited journal is worth more than one that receives few citations.

How it’s calculated: The number of citations in one year to content published in the previous five years (weighted)/ The number of articles published within the previous five years.

Altmetric Attention Score

 Altmetric Attention Scores tracks the online shares and conversations relating to a piece of published research. Each online ‘mention’ of that research is weighted differently. So, a journal article referred to (or ‘mentioned’) in an international newspaper is given more weighting in the overall Altmetric Attention Score than someone tweeting about the same piece of research.

How it’s calculated: Gathers data collected around research articles that aren’t usage or citation data, such as mentions on social media, in news outlets, on blogs, in policy documents or patents, and in online reference managers.