The h-index in a nutshell

 

by Shorba Harkhu

As a librarian you would have come across the metric h-index when searching or teaching the Web of Science or Scopus database. I must admit I had a fleeting understanding of the h-index. Attending the library postgraduate training sessions recently suddenly piqued my interest in this metric, and spurred me on to explore more.

When did it all start?

Jorge Hirsch in 2005, developed the h-index to measure and compare the overall scientific productivity of individual scientists (Barnes, 2017). The h-index can be regarded as a measure of the number of publications published (productivity) as well as how often they are cited (impact) (Stellenbosch University Library and Information Service, 2020).  It is based on the assumption that the number of papers should not be the only important factor in measuring a researcher’s impact in their field (Barnes, 2017). 

It involves some calculations

To calculate the h-index, only two pieces of information are required: the total number of papers published and the number of citations for each paper. Where these two numbers intersect is the h-index. For instance, a researcher with 17 published articles, each of which has received at least 17 citations, has an h-index of 17. If the researcher's 18th most cited publication was cited 16 times, the h-index remains at 17.

An explanation of the h-index in the Web of Science database

The h-index in the Web of Science is indicated by a dark purple horizontal line going through the columns, as in the illustration below. In the example below the number of items above this line means that there are 16 articles that were cited 16 times or more. Web of Science focuses on the last 4-5 years. If you add up the citations for record number 15 from 2017-2021, you will get a figure of 13, but if you click on the Back button (above 2017 in the illustration below) you will see the other citation counts for previous years, and once tallied will give you a total of 17 citations for that particular paper.

H-indexes differ from one database to another

Each database is likely to produce a different h-index for the same researcher for various reasons. This is because the databases index different journals and cover different years. For instance, Scopus only considers work from 1996 or later, while the Web of Science calculates an h-index using all the years that an institution has subscribed to (University of Michigan Library, 2021).

What is a good h-index?

Hirsch proposes that after 20 years of research, an h-index of 20 is good, 40 is outstanding, and 60 is truly exceptional (Oswald, 2021).

The influence of the h-index

The index is routinely used by researchers in a wide range of disciplines to evaluate both themselves and others within their field (Soicer, 2015). It also makes it easy for non-experts to evaluate a researcher’s contribution to the field (Soicer, 2015).

Some limitations of the h-index

The h-index cannot be compared across disciplines or different subjects. For example, an h-index of 5 in the social sciences does not hold the same weight as a 5 in engineering (Makowka, 2021).  The h-index also strips out any information about author order. The result is that there is little information about whether you published an article in a top journal on your own or whether you were one member of a team (Soicer, 2015). The h-index is also open to manipulation through practices like self-citation.

I hope this blog would have provided some insight into the h-index metric.

 

BARNES, C. 2017. The h-index Debate: An Introduction for Librarians. The Journal of Academic Librarianship, 43, 487-494.

MAKOWKA, M. 2021. H-Index Using Web of Science and SCOPUS [Online]. Texas: University of Texas at Dallas Available: https://libguides.utdallas.edu/h-index-using-web-of-science-and-scopus [Accessed].

OSWALD, N. 2021. Does Your h-index Measure Up? [Online]. [S. l]: BiteSize Bio. Available: https://bitesizebio.com/13614/does-your-h-index-measure-up/ [Accessed].

SOICER, A. 2015. Explainer: what is an H-index and how is it calculated? [Online]. [S. l]: The Conservation. Available: https://theconversation.com/explainer-what-is-an-h-index-and-how-is-it-calculated-41162 [Accessed].

STELLENBOSCH UNIVERSITY LIBRARY AND INFORMATION SERVICE. 2020. Bibliometrics and citation analysis: Introduction to h-index [Online]. Stellenbosch: Stellenbosch University Library and Information Service. Available: https://libguides.sun.ac.za/c.php?g=742955&p=5316861 [Accessed].

UNIVERSITY OF MICHIGAN LIBRARY. 2021. Research Impact Metrics: Citation Analysis [Online]. Anne Arbor. MI: University of Michigan Library. Available: https://guides.lib.umich.edu/c.php?g=282982&p=1887449 [Accessed].