Output metrics consist of two types:

• Citation-based metrics, based on the number of times an output is cited, generally by other academic sources
• Alternative metrics, which include online citations to digital research or policy documents and usage-based indicators, such as views, downloads, comments, bookmarks, or mentions on social media.

The information on this page focuses on citation-based metrics; please visit our companion page for information on alternative metrics.

The simplest citation-based output metric is citation count, a measure of the number of citations an output has received. Citation counts can be found in many citation databases including Scopus, Web of Science and Google Scholar. Citation counts are easy to quantify but have a number of significant limitations:

• They are not comparable across disciplines where citations accumulate at different rates
• They do not take account of the age of an output - in many disciplines it takes time for citations to accrue
• They do not take account of the type of publication - different output types attract varying numbers of citations and accrue citations at different rates.