H-index (H Index): A Comprehensive Assessment of a Scientist's Impact

Guide for authors
Posted on 20-06-2025

H-index, or H index, is a widely used quantitative measure to assess the influence and productivity of a scientist, based on both the number of publications and the number of citations those publications receive. First proposed in 2005 by physicist Jorge E. Hirsch at the University of California, San Diego, the H-index quickly became a standard tool for evaluating academic achievement, especially in the natural sciences. Sometimes, this index is also referred to as the Hirsch index or Hirsch number.

How to Calculate the H-index

The H-index combines the quantity and quality of scientific works, reflected by the number of published papers and the times they are cited by other researchers. A scientist with an H-index of h means that out of their n publications, h publications have received at least h citations. To calculate the H-index, an author's papers are arranged in descending order of the number of citations. The H-index is the largest number such that the author has at least h papers with at least h citations. For example, consider a scientist with 7 papers, ranked in descending order of citations as follows: In this example, the scientist has 5 papers that have been cited at least 5 times. Therefore, this scientist's H-index is 5. To achieve an H-index of 6, the 6th paper would need at least 6 citations.

Significance of the H-index

The H-index is an important indicator of a scientist's influence within the academic community. A high H-index typically indicates that the scientist has made significant and widely recognized contributions in their field. This index can influence the recognition of scientific achievement, international collaboration opportunities, and career advancement. Jorge Hirsch proposed some reference standards for the H-index in theoretical physics in the United States:

  • Successful: H = 20 after 20 years
  • Outstanding: H = 40 after 20 years
  • Truly unique individual: H = 60 after 20 years

He also suggested that, in the United States, a scientist could be appointed as an associate professor with an H-index of around 12 and as a full professor with an H-index of around 18. A variant of the H-index is the H5-index, which is used to assess a scientist's influence within a specific timeframe (usually the most recent 5 years). The H5-index is calculated by counting the number of papers by a scientist that have received at least H citations within that period. The higher the H5-index, the greater the scientist's influence during that period. Google Scholar Metrics uses the H5-index to rank journals and other scholarly publications, helping to reflect the currency and modernity of research activities.

How to Look Up the H-index

The H-index and related metrics can be looked up through reputable scientific citation databases such as Web of Science, Scopus, and Google Scholar. However, due to varying coverage and selection criteria among these databases, search results may not be entirely consistent. Therefore, when comparing the H-index of scientists, it is important to consider the data source used.

Web of Science

  1. Log in to your Web of Science account.
  2. Select "Author Search" and fill in the author's information, affiliation, and research area.
  3. On the results page, select "Create Citation Report".
  4. The Citation Report will display the H-index, total citations, and average citations per publication.
  5. To exclude publications not authored by the individual, select those publications and click "Go".

Scopus

  1. Log in to your Scopus account and select "Author Search".
  2. Fill in the author's information, affiliation, and research area.
  3. Select the desired author by checking the box next to their name, then select "View citation overview".
  4. The citation overview interface provides information on the H-index and annual citations for publications.

Google Scholar

  1. Log in to your Google (Gmail) account and create a profile on Google Scholar Citations.
  2. After creating the profile, the list of papers, citation information, and H-index will be displayed on the profile interface.

It should be noted that the H-index is not the sole metric for evaluating scientific activity. Many other metrics are also used to assess different aspects of scientific work, including:

  • i10-index: Measures the number of papers by an author that have at least 10 citations.
  • g-index: Measures the number of papers by an author that have at least g average citations.
  • e-index: Measures the effectiveness of cited papers by considering the ratio between the number of cited papers and the total number of published papers.
  • SJR (SCImago Journal Rank): Measures the importance of a scientific journal in its field, based on an analysis of citations from other reputable journals.