Eugene Garfield, the founder of the Institute for Scientific Information (ISI), first proposed the notion of citation indexing and journal impact factors in a 1955 article in Science magazine, and further explained impact factor in a 1972 article, also in Science. ISI is now owned by Thomson Reuters, and they explain impact factor as the "ratio between citations and recent citable items published. Thus, the impact factor of a journal is calculated by dividing the number of current year citations to the source items published in that journal during the previous two years."
Needless to say, there are those who object to relying on JIF (journal impact factor) to determine a journal's quality or importance, or an author's reputation. A 2016 article on the Science magazine website points out that, "for the articles published in any given journal, the distribution of citations is highly skewed. A small fraction of influential papers get most of the citations, whereas the vast majority of papers get few or none at all. So the average number of citations is often highly misleading." A 2014 article observes that, "the JIF is not representative of the impact of individual articles; an article published in a high-impact journal shouldn’t automatically be assumed to be of great importance or quality." Just type "impact factor" and "criticism" into a library database or search engine, and you will find numerous articles.
Another point of contention is that even though there are hundreds or even thousands of journals published in some fields, Journal Citation Reports (JCR) is highly selective in deciding which journals to track. As a 2004 article notes, "Unfortunately, despite good intentions, this selectivity on ISI's part has the unintended consequence of concealing the success of new journals." There is also a bias toward the sciences and social sciences at the expense of the arts and humanities. And a 2013 study found that only 7.9 percent of the titles included in JCR were Open Access (OA) journals.
Another measure of an author's impact is the h-index (developed by the scientist Jorge E. Hirsch). The h-index reflects an author's total number of publications as well as the number of citations per publication: a scholar with an index of h has published h papers, each of which has been cited at least h times in other papers.
The rise of social media has led to "altmetrics," which attempts to quantify the impact that an author or article has through the number of times it has been shared via social media, such as blog posts, tweets, downloads. One company that offers altmetrics is Plum Analytics, and after being acquired by EBSCO, Plum altmetrics data is now offered (where available) in EBSCO databases.
Bladek, M. (2014, April). DORA: San Francisco Declaration on Research Assessment. College & Research Libraries News 75(4), 191-196.
Bohannon, J. (2016, July 6). Hate journal impact factors? New study gives you one more reason. Science magazine website.
Cockerill, M. J. (2004, July 12). Delayed impact: ISI's citation tracking choices are keeping scientists in the dark. BMC Bioinformatics 5, 93.
Cummings, J. (2013). Open access journal content found In commercial full-text aggregation databases and Journal Citation Reports. New Library World 114(3/4), 166-178. Author's submitted version available through the WSU institutional repository.
Garfield, E. (2005, September 16). The agony and the ecstasy – the history and meaning of the journal impact factor. International Congress on Peer Review and Biomedical Publication.
Garfield, E. (1972). Citation analysis as a tool in journal evaluation: Journals can be ranked by frequency and impact of citations for science policy studies. Science 178(4060), 471-479.
Garfield, E. (1955, July 15). Citation indexes for science: A new dimension in documentation through association of ideas. Science 122(3159), 108-111.
Howard, J. (2013, June 3). Rise of 'altmetrics' revives questions about how to measure impact of research. Chronicle of Higher Education online. Published in print edition on June 7, 2013, A6-A7.
Roemer, R. C. & Borchardt, R. (2015). Meaningful metrics: A 21st-century librarian’s guide to bibliometrics, altmetrics, and research impact. Chicago, IL: ACRL.
Scopus (2014, May 8). The Scopus h-index, what's it all about? Part I. Elsevier Scopus blog.
Scopus (2014, May 9). The Scopus h-index, what's it all about? Part II. Elsevier Scopus blog.
SCImago Journal & Country Rank is a freely accessible website that uses data from Scopus to analyze both journals and countries. Although the data is accessible from within Scopus, it can also be accessed directly through its own domain. It includes more journal titles than JCR.
Google Scholar Metrics ranks the top 100 publications in English and several other languages, based on the journals' h-index for articles that were published in the last five calendar years (h5-index). Users can select broad categories from the drop-down menu (such as Social Sciences) and then subcategories (such as Library & Information Science).
For authors, Google Scholar can track citations for your publications.
Journal Metrics (also known as CiteScore) is also based on data from Scopus, and ranks journals based on their CiteScore, which is the number of citations received by a journal in one year to documents published in the three previous years, divided by the number of documents indexed in Scopus published in those same three years. It is a freely accessible website.
ERIH PLUS, the European Reference Index for the Humanities and Social Sciences, only lists the most important and prestigious journals published within the European Union, and the journals must meet strict criteria for inclusion.
Developed by Prof. Mark Eaton at Kingsborough Community College, Open Journal Matcher is a free website that attempts to match the text of a draft abstract with the abstracts of the over 5,000 titles from the Directory of Open Access Journals. It ranks the journals by similarity and returns the top five matches.
JournalGuide is a free website that attempts to match journals to a paper's content, so that authors can identify the journals that might be interested in publishing their article.
Elsevier matches words from your title, abstract, and keywords to Elsevier journals.
Jane is a free website that attempts to match journals indexed in Medline to a paper's content, so that authors can identify the journals that might be interested in publishing their article.
Scopus allows the user to click on a journal name when viewing a citation to find out its CiteScore, as well as information based on SJR (SCImago Journal Rank), SNIP (Source Normalized Impact per Paper), total number of citations for the journal(s) during the year, total number of document published by the journal(s) during the year, percentage of documents published by the journal(s) that were not cited during the year, and percentage of documents published by the journal(s) that are review articles. Scopus also provides the number of times an article has been cited, as well as an author's h-index. One can also click on "Sources" in the upper right to browse the top journals by subject area.
Eigenfactor attempts to measure a journal's total importance to the scientific community, using information from Journal Citation Reports. Although the data is accessible from within JCR, it is also freely accessible directly through its own domain.
The April 2020 issue of The Charleston Advisor has a fascinating article - "Scopus CiteScore and Clarivate Journal Citation Reports" - that compares the two resources.
Journal Quality List is compiled and edited by Prof. Anne-Wil Harzing "to assist academics to target papers at journals of an appropriate standard." It currently includes journals in the areas of Economics, Finance, Accounting, Management, and Marketing, and the list can be downloaded for free.
Microsoft ranks journals in several different subject areas.