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Assessing Article and Author Influence

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Finding an Author's H-Index

The H-Index: A Brief Guide

What is the H-Index?

H-Index chart
http://commons.wikimedia.org/wiki/File:H-index.png

The h-index, created by Jorge E. Hirsch in 2005, is an attempt to measure the research impact of a scholar. In his 2005 article Hirsch put forward "an easily computable index, h, which gives an estimate of the importance, significance, and broad impact of a scientist's cumulative research contributions." He believed "that this index may provide a useful yardstick with which to compare, in an unbiased way, different individuals competing for the same resource when an important evaluation criterion is scientific achievement."

There has been much controversy over the value of the h-index, in particular whether its merits outweigh its weaknesses. There has also been much debate concerning the optimal methodology to use in assessing the index. 

In locating someone's h-index a number of methodologies/databases may be used. Two major ones are ISI's Web of Science and the free Harzing's Publish or Perish which uses Google Scholar data.

How is the H-Index Computed?

An h-index of 20 signifies that a scientist has published 20 articles each of which has been cited at least 20 times. Sometimes the h=index is, arguably, misleading. For example, if a scholar's works have received, say, 10,000 citations he may still have a h-index of only 12 as only 12 of his papers have been cited at least 12 times. This can happen when one of his papers has been cited thousands and thousands of times. So, to have a high h-index one must have published a large number of papers. There have been instances of Nobel Prize winners in scientific fields who have a relatively low h-index. This is due to them having published one or a very small number of extremely influential papers and maybe numerous other papers that were not so important and, consequently, not well cited.

Factors to Bear in Mind

  • As citation practices/patterns can vary quite widely across disciplines, it is not advisable to use h-index scores to assess the research impact of personnel in different disciplines.
  • The h-index is not very widely used in the Arts and Humanities.
  • H-index scores can vary widely depending on the methodology/database used. This is because different methodologies draw upon different citation data. When comparing different people’s H-Index it’s essential to use the same methodology.
    The h-index does not distinguish the relative contributions of authors in multi-author articles.
  • The h-index may vary significantly depending on how long the scholar has been publishing and on the number of articles they’ve published. Older, more prolific scholars will tend to have a higher h-index than younger, less productive ones.
  • The h-index can never decrease. This, at times, can be a problem as it does not indicate the decreasing productivity and influence of a scholar.

Using Harzing's Publish or Publish to Assess the H-Index

Publish or Perish utilizes data from Google Scholar. Its software may be downloaded from the Publish or Perish website. A person's h-index located through Publish or Perish is often higher than the same person's index located by means of ISI's Web of Science. This is primarily because the Google Scholar data utilized by Publish or Perish includes a much wider range of sources, e.g. working papers, conference papers, technical reports etc., than does Web of Science. It has often been observed that Web of Science may sometimes produce a more authoritative h-index than Publish or Perish. This tends to be more likely in certain disciplines in the Arts, Humanities and Social Sciences.

After you've launched the application, click on "Author impact" on top. Enter the author's name as initial and surname enclosed with quotation marks, e.g. "S Helluy". Then click "Lookup" (top right). You'll see a screen with a listing of S. Helluy's works arranged by number of citations. Above this listing is a smaller panel where one may see the h-index score of 17:


H-index of 17

However, it's often the case that there are works in the list that are not by the author you are assessing. This is more likely when the author's name is a common one. Accordingly, it is important to go through the list and deselect any works by the wrong author. This is simply done by unchecking the work to the left of the record:

unchecking box in interface
 

Publish or Perish uses Google Scholar data and these data occasionally split a single paper into multiple entries. This is usually due to incorrect or sloppy referencing of a paper by others, which causes Google Scholar to believe that the referenced works are different. However, you can merge duplicate records in the Publish or Perish results list. You do this by dragging one item and dropping it onto another; the resulting item has a small "double document" icon as illustrated below:

merged row indication in interface

Selected Further Reading

Using Web of Science to Assess the H-Index

If you are using ISI's Web of Science database to assess a h-index, it is important to remember that Web of Science uses only those citations in the journals listed in Web of Science. However, a scholar’s work may be published in journals not covered by Web of Science. It is not possible to add these to the database’s citation report and go towards the h-index. Also, Web of Science only includes citations to journal articles – no books, chapters, working papers etc.). Moreover, Web of Science’s coverage of journals in the Social Sciences and the Humanities is relatively sparse. This is especially so for the Humanities.

Select the option "Cited Reference Search" (on top). Enter the person’s last name and first initial followed by an asterisk, e.g. Helluy S* If the person always uses a second first name include the second initial followed by an asterisk, e.g. Franklin KT*.

screen shot

If other authors have the same name, it’s important that you omit their articles. You can use the check boxes to the left of each article to remove individual items that are not by the author you are searching. The “Refine Results” column on the left can also help by limiting to relevant “Organizations – Enhanced”, by “Research Areas”, by “Publication Years”.

When you've determined that all the articles in the list are by the author, S. Helluy, you're searching for click on “Create Citation Report” on the right. The h-index for S. Helluy will be displayed as well as other citation stats.

H-index for S. Helluy

Notice the two bar charts that graph the number of items published each year and the number of citations received each year.

bar charts of published items

If you wish to see how the person's h-index has changed over a time period you can use the drop-down menus below to specify a range of years. Web of Science will then re-calculate the h-index using only those articles added for those particular years.

h-index across selected years

Contemporary H-Index

Contending that Hirsch's H-Index does not take into account the "age" of an article, Sidiropoulos et al. (2006) came up with a modification, i.e. the Contemporary H-Index. They argued that though some older scholars may have have been "inactive" for a long period their h-index may still be high since the h-index cannot decline. This may be considered as somewhat unfair to older, senior scholars who continue to produce (if one has published a lot and already has a high h-index it is more and more difficult to incease the index). It may also be seen as unfair to younger brilliant scholars who have had time only to publish a small number of significant articles and consequently have only a low h-index. Hirsch's h-index, it is argued, doesn't distinguish between the different productivity/citations of these different kinds of scholars.

The solution of Sidiropoulos et al. is to give weightings to articles according to the year in which they're published. For example, "for an article published during the current year, its citations account four times. For an article published 4 year ago, its citations account only one time. For an article published 6 year ago, its citations account 4/6 times, and so on. This way, an old article gradually loses its 'value', even if it still gets citations." Thus, more emphasis is given to recent articles thereby favoring the h-index of scholars who are actively publishing.

One of the easiest ways to obtain someone's contemporary h-index, or "hc-index", is to use Harzing's Publish or Perish software.

Publish or Perish interface