Tag: h-Index

Different Between H-Index and Impact Factor

 The h-index and impact factor are two measures of research quality. The h-index evaluates a researcher’s or an author’s scientific productivity based on the number of published research papers and their citations. The impact factor evaluates the total number of articles cited within the Journal during the previous two years1. The h-index is the largest number h, so h articles have at least h citations each. It has been argued that the H index outperforms the impact factor for evaluation purposes.

That’s a very interesting question. The journal impact factor and h index are different in their fundamental design: The former is used to measure journal prestige, while the latter is used to measure researcher impact. Therefore, the two cannot be compared. Let me explain.

The journal impact factor measures the average number of citations received by articles published within a journal over a two-year period. It can be a reliable measure of journal reputation but does not measure the impact of individual articles or researchers.

On the other hand, the h index is designed to measure the scientific output of a researcher by considering a combination of the number of papers the researcher has published and the number of citations those papers have received. Thus it measures both your publication record and its impact.

Do you now see how the impact factor and h index cannot be compared because they serve different purposes?

Your colleagues are right though. As a researcher, it is more useful for you to calculate your h index than to use the journal impact factor as a measure of prestige. The h index can especially work to your advantage if you have published many papers. I understand that it is troublesome and time consuming to calculate your h index because it requires you to maintain a record of all your published papers and the citations they have received through timely searches on multiple databases. But this would be time and effort well spent because the h index is gaining popularity and is increasingly being considered by grant and tenure committees.

However, like the journal impact factor, even the h index has its limitations, and it is advisable for you to mention a combination of citation metrics—the impact factor of journals in which you have published, your h index, and other article-level metrics—on your grant applications or statements of purpose, so as to give people a holistic view of your impact as a researcher. 

What is h-Index

 The h-index is an author-level metric that measures both the productivity and citation impact of the publications, initially used for an individual scientist or scholar.

The h index was proposed by J.E. Hirsch in 2005 and published in the Proceedings of the National Academy of Sciences of the United States of America.[i]  The h index is a quantitative metric based on analysis of publication data using publications and citations to provide “an estimate of the importance, significance, and broad impact of a scientist’s cumulative research contributions.”[ii]   According to Hirsch, the h index is defined as: “A scientist has index h if h of his or her Np papers have at least h citations each and the other (Np – h) papers have ≤h citations each.”

How Calculated: Number of papers (h) that have received at least h citations. 

As an example, an h index of 10 means that among all publications by one author, 10 of these publications have received at least 10 citations each.  

Hirsch argues that the h index is preferable to other single-number criteria, such as the total number of papers, the total number of citations and citations per paper. However, Hirsch includes several caveats:

  • A single number can never give more than a rough approximation to an individual’s multifaceted profile;
  • Other factors should be considered in combination in evaluating an individual;
  • There will be differences in typical h values in different fields, determined in part by the average number of references in a paper in the field, the average number of papers produced by each scientist in the field, and the size (number of scientists) of the field; and
  • For an author with a relatively low h that has a few seminal papers with extraordinarily high citation counts, the h index will not fully reflect that scientist’s accomplishments.[iii]
Hirsch stressed that the full career publications for an author should be used for the h index.

Since Hirsch introduced the h index in 2005, this measure of academic impact has garnered widespread interest as well as proposals for other indices based on analyses of publication data such as the g index, h (2) index, m quotient, r index, to name a few.

The h-index has already been used by major citation databases to evaluate the academic performance of individual scientists. Although effective and simple, the h-index suffers from some drawbacks that limit its use in accurately and fairly comparing the scientific output of different researchers. These drawbacks include information loss and low resolution: the former refers to the fact that in addition to h2 citations for papers in the h-core, excess citations are completely ignored, whereas the latter means that it is common for a group of researchers to have an identical h-index.

Several commonly used databases, such as Elsevier’s Scopus, Clarivate Analytics’ Web of Science, and Google Scholar  provide h index values for authors.