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What is the h-index?

In this article, we will talk about where the h-index comes from and how it is calculated. And with that background, we will be ready to put the h-index into context and discuss what it means to you as a researcher, where you can find it when you need it, and why it is important to seriously consider.

Knowing your h-index is an essential step to measuring the impact your research is having on your field and discipline. In this article, you will learn the basics of the h-index and how it applies to your research career.

You are getting your research out into the world, preprints, presentations, publications. People are reading it, discussing it, citing it. And you know this is important, not only for current projects but also for all those in the future.

How do you measure and share this exciting progress?

With so many metrics used to assess the quality and impact of your research, it can be hard to tell them apart. The h-index deserves some undivided attention, though. It is often used to rank candidates for grant funding, fellowships and other research positions.

In this article, we will talk about where the h-index comes from and how it is calculated. And with that background, we will be ready to put the h-index into context and discuss what it means to you as a researcher, where you can find it when you need it, and why it is important to seriously consider.

Background of the h-index

J.E. Hirsch first proposed the h-index in 2005 in his article An index to quantify an individual’s scientific research output. He argued that two individuals with similar hs would be comparable in terms of their overall scientific impact, even if their total number of papers or their total number of citations were very different (Hirsch, 2005). Making the metric an equalizer of sorts.

In practice, the total number of citations and papers are plotted on a graph like this (Wikimedia Commons, 2008). The h-index, then, is defined as the maximum value of h such that the given author or journal has published at least h papers that have each been cited at least h times (McDonald, 2005). Making an author’s greatest possible h-index limited to their total number of papers. As shown by the green square that is intersected by the dashed line on the graph.

In other words, an author with 1 paper that has 1 or more citations can have a maximum h-index of 1. In the same way, an author with several papers that each have 1 citation would also have a h-index of 1.

How do you calculate the h-index?

We can start by looking at the h-index in the simplest terms. If an author has 10 papers where each has at least 10 citations, then their h-index is 10. If, however, an author has five papers with 12, 6, 5, 2, and 1 citations respectively, then the author’s h-index is 3. This is because the author has only three papers with 3 or more citations. So, the h-index of 3 is where the h citations and the h papers would meet at the top corner of the green square in the graph we looked at above.

If you want to calculate an h-index manually, make a table with two columns. In the left column, assign ascending numbers beginning with 1 and going all the way to account for the author’s total number of papers. In the right column, arrange the number of citations for the author’s papers in descending order, where the biggest number is paired with the 1st paper.

Next, you move down the list until the paper number on the left is greater than the citation number on the right. Draw a line just above this position to look like the table below (MUHC Libraries, 2015). The h-index then equals the paper number just above the line. In this case the h-index is 8 because 8 articles have been cited at least 8 or more times. The remaining articles have been cited 8 times or less.

In this way, the h-index provides a more comprehensive view of the productivity and impact of a researcher’s work than the simpler metrics of the total number of papers or the total number of citations. And, at the same time, the h-index simplifies the same information by converting it into one easy to digest number.

h-index tools and resources

While knowing your h-index is useful, gathering all the data and calculating it yourself can be a pain. Fortunately, many of the resources you are already using to promote and track research papers offer convenient tools for generating h-index metrics.

It is a good idea to periodically check and compare your h-index from each of these resources. Chances are, the results will not match.

Each database calculates the h-index based only on the citations it contains. In the same way, software programs like Publish or Perish and management systems like Pure use a limited amount of citation data.

No single system retrieves and analyzes all citation information from all sources. This results in dissimilar h-index values. The databases also cover different journals over different ranges of years, which makes the h-index results vary.

Looking at how individual sources calculate your h-index and how it changes over time will help you recognize which of these is more accurate for your personal research career, field, and situation.

What is a good h-index?

Just as your h-index may vary from source to source, its weight and value are also on a sliding scale. An h-index number that is considered good in one area of research may only be subpar in another.

This is because every organization, institution, funding group, and hiring committee has its own set of requirements for any given research project or position. So, the idea of an acceptable or competitive h-index will change accordingly.

Many agree, however, that a satisfactory h-index will closely mirror the number of years a person has been working in their field. For example, h-index scores between 3 and 5 are common for new assistant professors, scores between 8 and 12 are standard for promotion to tenured associate professor, and scores between 15 and 20 are appropriate for becoming a full professor (Tetzner, 2021).

This is not a set guideline by any means. Rather a general explanation to use when setting your professional goals. That being said, you need to also stay current with your field’s practices regarding the h-index. And, always thoroughly check the h-index requirements for all applications you submit.

What are the pros and cons of the h-index?

Some people appreciate the h-index, some loathe it, and others have no opinion at all. Most who are familiar with the h-index, though, have a healthy level of respect while understanding that, like all metrics, it is imperfect.

Even at the dawn of its creation, Hirsch recognized the following advantages and disadvantages of his h-index (Hirsch, 2005):

Pros

  • It combines a measure of quantity (publications) and impact (citations).
  • It allows us to characterize the scientific output of a researcher with objectivity.
  • It performs better than other single-number criteria used to evaluate the scientific output of a researcher (impact factor, total number of documents, total number of citations, citation per paper rate and number of highly cited papers).
  • The h-index can be easily obtained by anyone.

Cons

  • There are inter-field differences in typical h values due to differences among fields in productivity and citation practices.
  • The h-index depends on the duration of each scientist’s career because the pool of publications and citations increases over time.
  • There are also technical limitations, such as the difficulty to obtain the complete output of scientists with very common names, or whether self-citations should be removed or not.
  • “A single number can never give more than a rough approximation to an individual’s multifaceted profile, and many other factors should be considered in combination in evaluating an individual (Hirsch, 2005).”

Final thoughts

During your research career, there will be many circumstances when you will inevitably have to interact with the h-index. Having a foundation of knowledge before that time comes is key to ensuring that your h-index is an asset and not a liability.

The information in this article will help you start laying the groundwork for clearly understanding the h-index. Where it comes from, how it is calculated, where to find it, and how it impacts your research career. It is one more vital step to ensuring that your valuable research finds its way out into the world.

References

Hirsch, J. E. (2005). An index to quantify an individual’s scientific research output. PNAS, 102(46), 16569-72. PMC. Retrieved Oct 26, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1283832/ McDonald, K. (2005, November 8). Physicist Proposes New Way to Rank Scientific Output. Phys.org. Retrieved October 26, 2022, from https://phys.org/news/2005-11-physicist-scientific-output.html MUHC Libraries. (2015, Jul 01). What’s your impact? Calculating your h-index | McGill University Health Centre Libraries. MUHC Libraries. Retrieved October 26, 2022, from https://www.muhclibraries.ca/training-and-consulting/guides-and-tutorials/whats-your-impact-calculating-your-h-index/ Tetzner, R. (2021, September 3). What Is a Good h-Index Required for an Academic Position? Journal-Publishing.com. Retrieved October 27, 2022, from https://www.journal-publishing.com/blog/good-h-index-required-academic-position/ Wikimedia Commons. (2008, Feb 01). File:h-index-en.svg. Wikimedia Commons. Retrieved October 26, 2022, from https://commons.wikimedia.org/wiki/File:h-index-en.svg

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