Measuring the value of research and scholarship is an important but extremely difficult to task.  Impact is best understood as a story–with many characters, settings, audiences, and lessons–that metrics help tell.  Metrics, such as citation analysis, help demonstrate value, but they can’t possibly make up the complete picture of any researcher’s impact nor any study’s value.  Impact, productivity, and performance are complex.  Relying on one single number or factor to assess any of these is problematic and very likely to be misleading.

Given the caveats above, the following are the most commonly used types of impact metrics, usually related to number of citations:

• Journal-level metrics
• Researcher-level metrics
• Article-level metrics (usually in the sciences and social sciences)
• Monograph-level metrics (usually in the humanities)
• Alternative metrics (new developments in bibliometrics and scientometrics)