The “Most Prolific” ranking is based on the number of unique papers attributable to a given author published during the period between 1 January 1985 and 21 April 2008 which mention Alzheimer’s Disease at least once in the Title, Abstract, or Key-Words and which are indexed in either the Thomson Web of Science or MEDLINE (i.e., PubMed) databases.

The “Most Frequently Cited” ranking is the sum total of all citations (as of 21 April 2008) to all papers attributable to a given author as described in the “Most Prolific” section above. The citation counts were taken from the Web of Science.

The “H-index” is a metric devised in 2005 by University-of-California-San-Diego physicist, Jorge E. Hirsch and described in a paper appearing in the Proceedings of the National Academy of Sciences of the United States of America. Here is Hirsch’s definition of the H-Index,

“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.”

In other words, a scientist with an H-index of 65 has 65 papers each of which has been cited at least 65 times.

The appeal of this metric is that with a single integer, one is able to get a sense of how productive a given scientist is considering only that scientist’s highest-impact papers. It is a metric which combines measures of quality and quantity and specifically does not assign credit to those authors who have produced many papers with few citations or those authors who were able to generate high total citation counts through only a handful of blockbuster papers.

Although only recently introduced, the H-Index is already being used in promotion-and-tenure decisions at major research universities as part of the scientific evaluation of faculty members.

The “H” in “H-Index” stands for the last name of the inventor i.e. “Hirsch.”