In 2005 Hirsch suggested a new measure to assess researchers' productivity and their academic impact. The h-index is defined as "a scientist has index h if h of his/her Np papers have at least h citations each, and the other (Np-h) papers have no more than h citations each". Harzing (2007) cites Glänzel, (2006) and reports "… the advantage of the h-index is that it combines an assessment of both quantity (number of papers) and quality (impact, or citations to these papers)". Since 2005 some researchers have measured h-index in different field. For example: Oppenheim, C. (2007). "Using the h-index to rank influential British researchers in information science and librarianship." JSIST, 58(2), 297-301.
However, h-index is not enough to measure the impact of someone's works in a field. In other words, though h-index is more appropriate than other methods including the total number of citations, the total number of papers and citations per paper, it has its own deficiencies. For example, junior researchers will inevitably have small h-index but it does not necessarily mean they are less productive. To improve these problems new supplementary measures have been proposed which are (1) m-index (accounting for varying lengths of academic careers), (2) g-index(accounting for highly-cited papers), (3) contemporary h-index (accounting for active versus inactive researchers), (4) individual h-index (accounting for differences in co-authorship patterns). To find out about these issues please have a look at the paper entitled "Reflections on the h-index" by Dr. Anne-Wil Harzing.