The h index was proposed by J.E. Hirsch in 2005 and published in the Proceedings of the National Academy of Sciences of the United States of America.[i] The h index is a quantitative metric based on analysis of publication data using publications and citations to provide “an estimate of the importance, significance, and broad impact of a scientist’s cumulative research contributions.”[ii] According to Hirsch, the h index is defined as: “A scientist has index h if h of his or her Np papers have at least h citations each and the other (Np – h) papers have ≤h citations each.”
As an example, an h index of 10 means that among all publications by one author, 10 of these publications have received at least 10 citations each.
Hirsch argues that the h index is preferable to other single-number criteria, such as the total number of papers, the total number of citations and citations per paper. However, Hirsch includes several caveats:
Since Hirsch introduced the h index in 2005, this measure of academic impact has garnered widespread interest as well as proposals for other indices based on analyses of publication data such as the g index, h (2) index, m quotient, r index, to name a few.
Strengths of the h index
Shortcomings of the h index
The m value is a correction of the h index for time (m = h/y). According to Hirsch, m is an “indicator of the successfulness of a scientist” and can be used to compare scientists of different seniority. The m value can be seen as an indicator for “scientific quality” with the advantage (as compared to the h index) that the m value is corrected for career length.
Other works that discuss the h index in comparison to various medical specialties are noted here.