Agarwal defines it as the process of extracting measureable data through statistical analysis of published research studies and how the knowledge within a publication is used.
These comprise the statistical analysis of citation counts, the number of times research, eg. an article, is cited by other works.
Measures include download counts and site hits as well as link analysis and web citation analysis - also referred to as scientometrics or cybermetrics
Altmetrics can be defined as metrics that are alternative to the established citation counts and usage statistics – and/or metrics about alternative research outputs, as opposed to journal articles”
The h-index attempts to measure both the productivity and impact of the published work of a researcher. The index is based on the set of the researcher's most cited papers and the number of citations that they have received in publications
JOURNAL IMPACT FACTOR
This measures the importance of a journal and the frequency with which the'average article' in a journal has been cited in a particular year or period. The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the two previous years. An Impact Factor of 10 means that on average the articles published during the previous two years ago have been cited ten times each.
MEDIAN IMPACT FACTOR
The Median Impact Factor is the value of all journal impact factors in the subject category. The Median Impact Factor mitigates the importance of absolute citation frequencies. It tends to discount the advantage of large journals over small journals, as well as frequently issues over less frequently issued journals. It is a valuable tool for journal evaluation, because the journal impact factor offsets the advantages of size and age.
The Immediacy Index is the average number of times an article is cited in the year it is published. The Journal Immediacy Index indicates how quickly articles in a journal are cited and the Aggregate Immediacy Index indicates how quickly articles in a subject category are cited. The Immediacy Index is calculated by dividing the number of citations to articles published in a given year by the number of articles published in that year.
The Eigenfactor Score measures the number of times articles from the journal published in the past five years have been cited in the JCR year. The Eigenfactor Score is essentially a ratio of the number of citations to the total number of articles. Unlike the Impact Factor the Eigenfactor Score counts citations to journals in both the sciences and the social sciences and eliminates self-citations.
ARTICLE INFLUENCE SCORE
The Article Influence Score measures the relative importance of the journal on a per-article basis. It is the journal's Eigenfactor Score divided by the fraction of articles published by the journal. That fraction is normalised so that the sum total of articles from all journals is 1. The mean Article Influence Score is 1.00. A score greater than 1.00 indicates that each article in the journal has above average influence. A score less than 1.00 indicates that each article in the journal has below average influence.
Scopus CiteScore is the average citations per document that a title receives over a three-year period.
SCIMAGO JOURNAL RANK (SJR)
SCImago Journal Rank (SJR) is a prestige metric based on the idea that ‘all citations are not created equal’. With SJR, the subject field, quality and reputation of the journal has a direct impact on the value of a citation. This means that a citation from a source with a relatively high SJR is worth more than a citation from a source with a lower SJR.
SNIP (SOURCE NORMALIZED IMPACT PER PAPER)
Scopus SNIP (Source Normalized Impact per Paper) measures contextual citation impact by weighting citations based on the total number of citations in a subject field. The impact of a single citation is given higher value in subject areas where citations are less likely, and vice versa.