Tools for Authors: What is the h index?

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:

• A single number can never give more than a rough approximation to an individual’s multifaceted profile;
• Other factors should be considered in combination in evaluating an individual;
• There will be differences in typical h values in different fields, determined in part by the average number of references in a paper in the field, the average number of papers produced by each scientist in the field, and the size (number of scientists) of the field; and
• For an author with a relatively low h that has a few seminal papers with extraordinarily high citation counts, the h index will not fully reflect that scientist’s accomplishments.[iii]

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.

Several commonly used databases, such as Elsevier’s Scopus, Clarivate Analytics’ Web of Science, and Google Scholar  provide h index values for authors.

Do you need an h index report?

We provide h index reports (Scopus and/or Web of Science) to members of the Washington University in St. Louis community.

Contact Amy Suiter to request a report.

Strengths of the h index

• The h index is a metric for evaluating the cumulative impact of an author’s scholarly output and performance; measures quantity with quality by comparing publications to citations.
• The h index corrects for the disproportionate weight of highly cited publications or publications that have not yet been cited.
• Several resources automatically calculate the h index as part of citation reports for authors.

Shortcomings of the h index

• The h index is a metric to assess the entire body of scholarly output by an author; not intended for a specific timeframe.
• The h index is insensitive to publications that are rarely cited such as meeting abstracts and to publications that are frequently cited such as reviews.
• Author name variant issues and multiple versions of the same work pose challenges in establishing accurate citation data for a specific author.
• The h index does not provide the context of the citations.
• The h index is not considered a universal metric as it is difficult to compare authors of different seniority or disciplines. Young investigators are at a disadvantage and academic disciplines vary in the average number of publications, references and citations.
• Self-citations or gratuitous citations among colleagues can skew the h index.
• The h index will vary among resources depending on the publication data that is included in the calculation of the index.
• The h index disregards author ranking and co-author characteristics on publications.
• There are instances of “paradoxical situations” for authors who have the same number of publications, with varying citation counts, but have the same h index. As an example, Author A has eight publications which have been cited a total of 338 times and Author B also has eight publications which have been cited a total of 28 times. Author A and Author B have the same h index of 5 but Author A has a higher citation rate than Author B. See Balaban, AT. 2012. Positive and negative aspects of citation indices and journal impact factors. Scientometrics. DOI: 10.1007/s11192-102-0637-5

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.

Per Hirsch:

• h index of 20 after 20 years of scientific activity, characterizes a successful scientist
• h index of 40 after 20 years of scientific activity, characterizes outstanding scientists, likely to be found only at the top universities or major research laboratories.
• h index of 60 after 20 years, or 90 after 30 years, characterizes truly unique individuals.
• h index of 15-20, fellowship in the National Physical Society.
• h index of 45 or higher, membership in the National Academy of Sciences.

Other works that discuss the h index in comparison to various medical specialties are noted here.