H-index is a citation-based metric that attempts to measure the influence of an individual researcher (or group of researchers, such as an institution) by considering both productivity and impact.
The h-index represents the point at which a scholar has h publications with h citations each—for instance, if a scholar has published 10 articles with at least 10 citations each, his h-index is 10.
H-index is an improvement over a simple count of total publications (which may have had no impact) or a total number of citations (which may be skewed by one particular project which had significant impact, even if no other projects showed any impact at all).
Much like Impact Factor, h-index should only be compared within a discipline but not between disciplines, since publishing and citing patterns vary among fields. Additionally, even within a field, one should keep in mind that the length of time in a field impacts h-index, and it thus favors senior researchers over junior researchers. However, h-index may prove particularly informative when used to compare a particular researcher to peers in his discipline who have a similar number of years working in the field.
H-index is freely available from Google Scholar at scholar.google.com for some researchers (if they have a Google Scholar Citations page; see the page later in this guide on how to create your own). H-index can be obtained from commercial tools such as the Web of Science database (Thomson Reuters), provided by the SHSU library. It can also be calculated with the free Harzing's Publish or Perish program, or the Scholarometer browser extension, both of which use Google Scholar data.
Here is an example of citation counts and an h-index score from a researcher's Google Scholar Citations page:
Researchers should be aware that there is some professional debate over h-index as a metric. Researchers should understand the potential pros and cons before deciding whether and to what extent to rely on this metric.
The following article, although targeted at librarians, may provide any researcher with a foundational understanding of this debate.