How does the scientific community measure how "good" or "great" a journal or an author is? How do you determine the "impact" of an author's work? Should it be purely based on the number of times the article is cited? If not, how can we measure the "quality" of the research?
Several methods to calculate the impact of an article, journal, or author have been developed answer these questions. These calculations and statistical methods are called metrics. Be aware metrics are highly debated. The most popular metrics include: number of citations (journal or author), journal impact factor, and author h-index. There are hundreds of other metrics available, some better defined than others.
According to Journal Citation Reports (JCR), an impact factor is a ratio focusing on original research.
Impact factor = # of citations to all items published in that journal in the past two years
# of articles and reviews published over those past two years referencing those citations
For example, if a journal has an impact factor of 2.5, this means in the indexed year each article published was cited on average 2.5 times in the previous two years in that journal.
Impact factor is used for journals only.
JCR only includes 12,000 journals and conference proceedings from over 3,300 publishers.
The most common metric to track an author's impact is ask how often they are cited. However, for the information to be accurate, a database must:
We may be able to get close, but
Thus, no one database can give an accurate count of how many times an individual article (much less the author) has been cited!
The h-index attempts to measure both the productivity and impact of an author. H is the number of articles published by an author which have each been cited at least h times. (E.g., an author published 4 papers that are cited 10, 6 ,5 and 2 times respectively; that author's h-index is 3.)
Recently, some databases (e.g. Google Scholar) use an h-index for the journal. In this case, h is the number of articles published that have been cited h times over a given time period (H5 = five years).
Metrics on the Web
The question "how many times has this article been cited?" has no simple answer. This number depends entirely on the database used and how the article references are searched by that database. Take, for example, for the article:
Age differences activity during emotion processing: reflections of age-related decline or increased emotion regulation? by Kaoru Nashiro, Michiko Sakaki, and Mara Mather.
On May 1, 2017:
Each database or search engine has its strengths and limitations. Some (e.g. Google Scholar and ResearchGate) include duplicate listings in their citation numbers. To identify all of the articles, letters, dissertations and books that cite a specific article, it may be necessary to search multiple databases and keep your own records.