Used to determine the citation impact of authors, articles, and journals. Beyond basic citation counts, there are measures such as the h-index and the g-index which are used to quantify the impact of an individual author.
Employing usage data such as the number of downloads for an article. Researchers are now looking at whether download statistics could be used to predict future citations (SLU).
Journal Impact Factor:
The method of ranking journals within a discipline or a sub-discipline, or to determine the average citation count for a journal use. (Garfield, 2005)
There is a growing movement calling for the inclusion of measurements of scholarly impact drawn from the social web, which is likely to grow as the "born-digital" generation moves towards and into tenured positions. This has been termed "Altmetrics."
What is the effect of Open Access on citations?
A number of studies have now proved there is a measurable increase in citation impact for open access articles. The size of the increase varies and depends on the year and on the discipline (Open Access Scholarly Information Sourcebook).
This chronological bibliography focuses on the relationship between open access and impact.
This article, featured in PLOS One Collections, outlines how scholars find and often cite high-quality work, whether a college or university mandates scholars to put their work in a publicly accessible website, or the scholars are free to self-archive as little or as much as they want (Gargouri et al).