What Is H-Index? Everything You Need to Know About Research Impact Metrics

Research impact is a term used to describe the influence of a scholar’s work. Research impact metrics are quantitative methods used to measure the research impact of individual researchers, a group of scholars, or that of a scientific journal. Examples of impact metrics include citation count, journal impact factors, the h-index, and others.

The primary purpose of the h-index is to evaluate the cumulative impact of an individual’s scholarly work. It compares author’s publications to citations, measuring quantity with quality. This article outlines all there is to know about the h-index.

The H-index can not only be computed for a researcher but also for a journal, analogously

What Is H-Index?

The h-index was invented by Jorge E. Hirsch, an Argentine American physics professor at the University of California. The term was first used in the official journal of the National Academy of Sciences of the U.S. in 2005.

Hirsch believed that the relevance and impact of Nobel prize winners was unquestionable. Hence, he was looking for ways to quantify the cumulative impact and relevance among the rest of the scholars.

That’s when he came up with the h-index. The h-index is a quantitative research impact metric based on publication data analysis. The analysis relies on publications and citations and aims to analyze the significance and impact of an author’s cumulative research contributions.

To calculate the h index, we take into account the number of articles (h) with at least h citations. As an example, a researcher with an h-index of 14 has written at least 14 papers, each having received at least 14 citations.

The advantage of the h-index is that it combines the measure of quantity and impact in one indicator. It’s also more efficient than other one-dimensional criteria for evaluating a researcher’s scientific input (number of citations, impact factor, number of highly cited papers).

Here are more details on how to calculate the h-index.

Calculating H-Index

To calculate the h-index of an author, their publications are ordered by the number of citations they have received. The order goes from most to least cited. Imagine a researcher has published seven articles, cited as follows:

This researcher has an h-index of 4, because four or more articles received four or more citations. However, you may notice that the mean number of citations is higher. The h-index reduces the weight of highly cited papers.

The h-index of a journal listed in Scimago, for example, is also relevant.

Where to Find the H-Index Online?

There are plenty of online resources where you can calculate your h-index:

• Google Scholar provides this metric for researchers who create a profile on the platform.
• Publish or Perish analyzes Google Scholar citations and offers h-index metrics as well. It’s also good software for finding the h-index if you don’t have a Google Scholar profile.
• Scopus has a citation tracker tool that generates the h-index for publications from 1970 to current.
• Web of Science generates h-index metrics for works from 1970 to current with their “Create Citation Report” tool.

Ever since it was introduced, the h-index has been the subject of widespread interest. Other research impact metrics such as g-index and i10-index were introduced as a result.

G-Index

The g-index gives more weight to the highly-cited papers of a researcher compared to the h-index. It’s also among the most complex metrics to calculate.

This metric is calculated when the top g articles (ranked by citations) from a specific author receive at least g² (g squared) citations. For example, an author with a g-index of 15 indicates that their top 15 publications have been cited at least 225 times (15²). Or an author with a g-index of 30 means their top 30 publications have been cited at least 900 times (30²).

I-10 Index

The i-10 index is the most recent research impact metric introduced by Google Scholar. It measures the number of publications that received at least ten citations. It’s the most straightforward metric to understand and calculate. However, it’s only used for works in Google Scholar.

What Is a Good H-Index?

A good h-index value varies from field to field.

Surveys among academic physicians show that assistant professors have an average h-index of two to five, associate professors six to ten, while full professors have an h-index from 12 to 24.

The world’s highest h-index scores come from researchers from top universities like Oxford or Harvard.

Scientists with High H-Indexes

At the time of writing, the highest score recorded by Google Scholar is 300, by researcher Ronald C Kessler from Harvard University. JoAnn E Manson from Brigham and Women’s Hospital takes second place with a score of 294. The third place goes to Graham Colditz from Washington University in Saint Louis with an h-index of 293.

Google Scholar’s list features over 4,700 researchers with an h-index of at least 100.

Nobel Prize winners are also among the most-cited researchers, but the number of citations among them varies. For example, the 2012 Nobel Prize winner in chemistry, Robert J. Lefkowitz, has an h-index of 237 on Google Scholar. The 2012 economic science Nobel Prize winner Alvin E. Roth has a score of 103 on the same platform.

Building a Good H-Index

Building a good h-index takes time and effort. However, you can follow the tips below to get there faster:

• The most important tip to building a good H-index is to produce top-quality research of high significance.
• Collaborate with experienced researchers. Studies show that articles with renowned first authors receive more citations. This tip is especially useful for those who are only starting their careers.
• Pick the right journal. Publishing in established journals will attract more readers, leading to more citations.
• Go open access. Open access journals receive more citations due to the mere fact they’re freely available across the web.
• Have the audience in mind. Pick a journal according to its audience. Publishing in specialist journals can get you more citations from same-field researchers.
• Work on your networking. Attend webinars or conferences whenever possible. This helps promote new work and meet potential collaborators.
• Spread the word across the web. Make a social media page if you don’t already have one. Consider starting a blog, so other researchers can easily find you and your work.

What Can Be the Disadvantages of H-Index?

Although functional, the h-index is certainly not the most objective research impact metric. Here are some of its limitations:

• The h-index shouldn’t be used to compare researchers from different fields. The metrics are often higher in some fields (like economics) and lower in others (like literary criticism). The reason lies in the differences in overall field productivity and citation practices.
• The h-index is highly dependent on the duration of an individual’s career. The number of citations increases over time as the researcher’s publications grow in number. For this reason, young researchers can’t be compared to more experienced researchers. The “m parameter” is the alternative metric that divides the author’s h-index by their scientific age (years since their first published article).
• Open for manipulation. Authors can cite their own past works to increase their h-index. Also, a common practice between researchers is to cite each other’s work routinely, further manipulating the metrics.
• The fact that the h-index is easy to obtain imposes the risk of indiscriminate use. It’s wrong to rely only on this factor when assessing an author’s scientific research output.
• Scientists who publish a small number of highly influential articles receive a small h-index.

Choose AKJournals to Help with Your Articles

The research impact of an author is often measured with the h-index. Researchers use this metric to evaluate themselves but also others within their fields. Although it has more than a few disadvantages, the h-index is still one of the most popular research impact metrics. With it, even non-experts can evaluate an author’s contribution to a field.

To get a higher h-index, it’s important to publish in established journals with a broad audience. AKJournals offers just that. We are Hungary’s oldest continuously running publishing house and among the most prominent scientific publishers in Central and Eastern Europe. Publishing in our journals means your work is brought closer to a thriving community of researchers, resulting in more citations and a higher h-index score.