Citation analysis, also called citation tracking or cited reference searching, involves identifying articles, books, or other materials that have cited a specific work. Citation analysis helps determine how much impact a particular scholarly work has had. There are a number of tools available; however, no single database covers all works that cite other works. Searching across several databases is necessary to ensure complete coverage.
Discipline -- "social science and humanities disciplines tend to cite more slowly...Citation metrics should not be compared across disciplines unless this is accounted for..."
Document Type -- "Review papers tend to attract the most citations; case studies tend to attract the fewest citations."
Age of Research Cited -- "Older articles [and older researchers] will have more citations."
Data Source -- The number of citations will vary from one data source to another (i.e. Web of Science, Google Scholar, etc.).
Neophytou, J. (2014). How to navigate the world of citation metrics. Wiley Exchanges. Retrieved from http://exchanges.wiley.com/blog/2014/05/15/how-to-navigate-the-world-of-citation-metrics/