What is h-Index

 The h-index is an author-level metric that measures both the productivity and citation impact of the publications, initially used for an individual scientist or scholar.

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.”

How Calculated: Number of papers (h) that have received at least h citations. 

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]

Hirsch stressed that the full career publications for an author should be used for the h index.

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.

The h-index has already been used by major citation databases to evaluate the academic performance of individual scientists. Although effective and simple, the h-index suffers from some drawbacks that limit its use in accurately and fairly comparing the scientific output of different researchers. These drawbacks include information loss and low resolution: the former refers to the fact that in addition to h2 citations for papers in the h-core, excess citations are completely ignored, whereas the latter means that it is common for a group of researchers to have an identical h-index.

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