Understanding the h-Index

A Primer

Published in

On Economics

5 min readJun 18, 2024

What is the h-Index? How is it calculated? What are its strengths and weaknesses? Read on to find out.

The h-index is a metric designed to quantify both the productivity and citation impact of the publications of a researcher. It was introduced in 2005 by Jorge E. Hirsch, a physicist at UC San Diego, as a tool for determining theoretical physicists’ relative quality.

Since then, it has been widely adopted in various scientific disciplines as a means of measuring the academic influence of researchers.

How is the h-Index Calculated?

The h-index is calculated based on the set of a researcher’s most cited papers and the number of citations that they have received in other publications. Specifically, a scholar with an index of h has published h papers each of which has been cited in other papers at least h times. 4

Thus, if a researcher has an h-index of 10, this means that they have 10 papers that have each received at least 10 citations.

Suppose a researcher has the following numbers of citations for their top 10 papers: 50, 40, 30, 25, 20, 15, 10, 8, 5, and 3. The h-index is 8 because the researcher has 8 papers with at least 8 citations each.

Strengths

Combines Quantity and Quality: The h-index reflects both the number of publications and the number of citations per publication. This differs from total citation counts which do not account for the number of publications, and from publication counts which do not account for the impact of each publication.
Robustness: Once achieved, the h-index does not decrease even if a researcher’s papers do not accumulate more citations. This provides a durable measure of a scholar’s cumulative impact and productivity.
Simplicity: The h-index is straightforward to calculate and easy to understand. It provides a single figure that can help in comparing the scholarly output of researchers.

Weaknesses

Age Bias: It tends to favor researchers who have been active for a longer time. New researchers or those in early stages of their career might have low h-index scores despite significant impacts in their fields.
Discipline Sensitivity: Citation behaviors vary widely between different fields. For example, theoretical mathematics tends to have fewer citations per paper than biomedical research. Thus, the h-index may not uniformly reflect impact across different disciplines.
Omission of Context: The h-index does not account for the context of citations. Citations used to critique or refute a paper are counted equally as those that support the work.
Neglect of Highly Influential Papers: Researchers with one or several extremely highly cited papers may not have a correspondingly high h-index if their other papers have few citations.
The h-index might also be gamed, in various ways. See next section.

Gaming the h-index

Self-Citations: Researchers might excessively cite their own work in new publications. By doing so, they artificially inflate the number of citations each of their papers receives, thereby potentially increasing their h-index
Collusive Citations (“Citation Cartels”): This involves a group of researchers agreeing to cite each other’s work regardless of its relevance to the topic of their publication. Such reciprocal citation practices can significantly boost the citation counts for all involved, manipulating their h-index scores.
Salami Slicing: This tactic involves breaking down a single substantial piece of research into several smaller chunks and publishing them as separate papers. While each paper may not be very impactful by itself, this strategy can increase the number of publications that might each receive citations sufficient to count towards the h-index
Choosing Low-Impact or Easy Journals: Publishing in journals that may have lower standards for acceptance can be a strategy to quickly boost publication numbers. If these journals are still cited within the community, this can lead to an increase in the h-index.
Strategic Authorship: Adding one’s name to a high number of collaborations, even if the contribution is minimal, can also increase the number of papers attributed to a researcher. Being part of large research groups or networks where the norm is to include all members as co-authors on publications can inflate one’s h-index.

Applications

Academic Evaluations: Universities and other academic institutions often use the h-index as a criterion when evaluating the performance of faculty members for tenure and promotion. A higher h-index can indicate significant research impact and productivity, which are key considerations in these decisions.
Grant Funding: Funding bodies may consider a researcher’s h-index to assess their track record and the likely impact of their future work when deciding on grant allocations. Researchers with a higher h-index are often perceived as more likely to contribute impactful research, potentially influencing the allocation of research funds.
Awards and Honors: The h-index is sometimes used as one of the metrics to determine the eligibility and selection of candidates for awards and honors in scientific communities. These can include prestigious fellowships and membership in professional societies that recognize research excellence.
Job Recruitment: Academic and research institutions might look at a candidate’s h-index as part of the hiring process, especially for positions that require a proven research background. A higher h-index can be an advantage for candidates applying for research-focused roles.
Research Collaborations: When looking for potential collaborators, researchers and institutions might use the h-index as a quick measure of a scientist’s influence and expertise in their field. A higher h-index might indicate a fruitful collaborator who can contribute significantly to joint research endeavors.

Concluding Caveats

While the h-index is a useful tool for assessing research impact, it should not be used in isolation. It’s important to consider a variety of metrics and a comprehensive evaluation of a researcher’s contributions and influence in their field. The context of citations, the nature of the publication, and the norms of the specific academic discipline all play critical roles in accurately assessing scholarly impact.