Citation index numbers provide a way to measure impact beyond raw citation counts. Index numbers can be calculated for individual articles, a group/list of publications, or even all the articles published in a journal or field (see our Journal Impact page).
Generally, the "best" measurement depends on what matters to you. The h-index is the most widely known index measurement. Some alternative measurements, like the g-index, address specific issues with the h-index. Other measurements target recent publications and citations, such as the the contemporary h-index.
Alternatives to the h-index include:
For more index measurements, we suggest "Reflections on the h-index," by Prof. Anne-Wil Harzing, University of Melbourne.
The h-index attempts to correlate a researcher's total publications and total citations. It was proposed by Jorge E. Hirsch in 2005 ("An index to quantify an individual's scientific research output," PNAS November 15, 2005 vol. 102 no. 46 16569-16572). For more information, see the Wikipedia article.