Q. What is an h-index? How do I find the h-index for a particular author?

The h-index is a number intended to represent both the productivity and the impact of a particular scientist or scholar, or a group of scientists or scholars (such as a departmental or research group). 

The h-index is calculated by counting the number of publications for which an author has been cited by other authors at least that same number of times.  For instance, an h-index of 17 means that the scientist has published at least 17 papers that have each been cited at least 17 times.  If the scientist's 18th most cited publication was cited only 10 times, the h-index would remain at 17.  If the scientist's 18th most cited publication was cited 18 or more times, the h-index would rise to 18.

Part of the purpose of the h-index is to eliminate outlier publications that might give a skewed picture of a scientist's impact.  For instance, if a scientist published one paper many years ago that was cited 9,374 times, but has since only published papers that have been cited 2 or 3 times each, a straight citation count for that scientist could make it seem that his or her long-term career work was very significant.  The h-index, however, would be much lower, signifying that the scientist's overall body of work was not necessarily as significant.

The following resources will calculate an h-index:

Scopus

Web of Science

Pure (MD Anderson Faculty and Fellows listed)

Keep in mind that different databases will give different values for the h-index.  This is because each database must calculate the value based on the citations it contains.  Since databases cover different publications in different ranges of years, the h-index result will therefore vary.   You should also keep in mind that what is considered a "good" h-index may differ depending on the scientific discipline.  A number that is considered low in one field might be considered quite high in another field.

A note about Google Scholar

Google Scholar usually provides the highest h-index compared to other sources. This is because Google Scholar indexes web pages not organized collections of article citations, like databases. This means Google Scholar:

• Counts all publications, including books
• Counts all versions of a paper it finds, including preprints
• Counts self-citations 
• Counts citations added manually, but not necessarily verified by a publisher or other source