Gerontology *: Impact Metrics

Available electronic collections, books and journals

What are metrics?

How does the scientific community measure how "good" or "great" a journal is? How do you determine the "impact" of an author's work? Should it be purely on the number of citations? Or is it a matter of the "quality" of the research? But then again, how do you measure "quality"?

These questions caused people to create methods on how to calculate the impact or "good-ness" of an article, journal, or author. These calculations and statistical methods are called metrics. Metrics are debated over, and over, and over. Most popular metrics include: number of citations, impact factor, and h-index. There are hundreds of other metrics available, some better defined than others. See the link below for more information about other available metrics.

Impact Factor

One metric used is impact factor. Impact factor is the average number of citations per article published in a given year. 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 more recent years.

*There is usually a delay in determining the most recent impact factor because publishers have to wait till at least one full year in order to calculate (or re-calculate) the impact factor.

Journal Citation Reports is a database that calculates out the impact factor for the major journals in science and engineering. JCR can provide a report of impact factor based on a specific journal title, a category of journals, or the highest impact factor (period).

Impact factor is used for journals only.


Journals have impact factor, authors have the h-index. h-index is somewhat complex calculation taking into account the total number of articles published by an author and the number of citations per article.

An author's h-index, or h, is equal to the number of total articles published, as long as every article has at least h number of citations.

h-index is used for authors only.

Article citations

It's easy to say "how many times has this article been cited?" However, there is 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 February 14, 2017:

  • In PubMed, this article was cited 31 times in PMC (an archival database, formerly PubMed Central)
  • Google Scholar reports: Cited by 87 (with 22 available versions) - the date is incorrect (2011), but the link is to the correct article
  • Scopus says Cited by 47 documents, while USC Summon notes only 10 citations in Scopus (because of the way the USC search works)
  • Web of Science reports the article was 35 times cited, which the publisher, Karger, then quotes; (to be complete, USC Summon only lists 34 citations)
  • ResearchGate reports 67 citations

To identify all of the articles, dissertations and books that cite an article, it may be necessary to search multiple databases.