H-index, Good or Bad?

As papers and journals are rated and validated by specific indicators, researchers are no exception. H-index is used to measure a researcher’s productivity and the impact of their published documents.

H-index

The h-index is an author-level metric that was invented in 2005 by Jorge Eduardo Hirsch, an Argentine-American professor of physics at the University of California, San Diego.

Hirsch is an index that attempts to measure both the productivity and citation impact of the publications of a scientist or scholar by number.

The h-index of a researcher is calculated by the total number of papers published (Np) and the number of citations (Nc) for each paper.

H-index Calculation

The h-index can be calculated manually or by using databases that index articles.

To calculate h-index manually, after searching the author’s name and seeing the results in different years, arrange his/her articles by citation in descending order and compare the number of articles with the number of citations until the number of citation be equal to or greater than the article number. The number of that article represents the author’s h-index. For example, if the author has published ten articles, six of which have been cited at least six times, the author’s h-index is six.

There are three popular databases that calculate the h-index:

Web of Knowledge (WOK)

The Web of Knowledge is one of the databases owned by the Institute for Scientific Information (ISI) and is one of the best tools for calculating the h-index. This tool takes into account all of an author’s articles from the beginning to the present, to calculate the h-index. If you have access to the site through a university or personal account, you can easily find the author’s name, the h-index and many other statistical information about him/her.

Scopus

This database is owned by Elsevier Publications and is another database that calculates the h-index and many other statistical information for various authors. Scopus only considers articles from 1995 onwards that are registered on this database.

Google Scholar

This database is owned by Google and is free and you can easily calculate the h-index with a Google account. Since Google Scholar considers a wide range of articles in the calculation of h-index (even free articles available online and not published in valid journals), is not accurate like the other two databases, but since it is a free tool and there are many widgets to use, it is convenient.

Differences Between Databases

For researchers who have devoted many years to research, the calculated hi-index by different databases can be significantly different.

This difference is due to some of the factors mentioned earlier. Some of the most important factors can be listed as follows:

The difference in the time of the article’s publication for index calculation: Since the Scopus database calculates h-index by considering articles from 1995 onwards that are registered on this database, the articles published before 1995 are overlooked, which may have been cited repeatedly. The effect of this difference is, therefore, more pronounced in the Scopus database.

The difference in article coverage: Sometimes an article may not be registered in a database for a variety of reasons. The effect of this difference, however, is usually not that significant. In addition, you can request changes to your articles using the facilities provided by Scopus and WOK. These two databases will reduce or increase the number of articles or citations you want after review.

The difference in the number of articles and name similarities: In the Scopus and WOK databases each author has a page for himself and all the information about him is recorded so that the probability of displacement in researchers’ articles is zero. On the other hand, each published article is registered only once in these databases. That’s not the case with Google Scholar. If there is a name similarity, it is possible to overlap, and this can sometimes cause differences in results. An article may also be listed two or more times in Google Scholar. Under certain conditions, this can lead to a false increase or decrease of the h-index.

Advantage of h-index

• Evaluates both qualitatively (impact factor or citations) and quantitatively (number of articles) and does not have the disadvantages of other ranking indices such as counting the total number of articles or the total number of citations.
• The Hirsch index provides a strong evaluation of the impact of a researcher’s scientific articles, meaning that it ignores low-citation or no-citation articles, or high-citation articles in computation.
• This index can be a good benchmark for evaluating researchers who have had a significant impact on scientific participation but their scientific work has not been given the opportunity using conventional scientometric channels.
• The data needed for computation of this index is easily accessible through the ISI, Scopus, and Google Scholar databases without the need for any information processing.

Disadvantages of h-index

• The number of authors of an article and the contribution each has to the research is not determined by this index.
• Some academic majors, and consequently some journals, have different ways of citing articles. Sometimes an article on agriculture has nearly a hundred references, but an article on mathematics has far fewer references than that, which is due to the difference between journals and scientific majors and H-index does not consider this issue.
• If a researcher has a limited number of papers but they are highly cited, the H-index will not be high.
• H-index does not review the citation text. Many articles may be cited in one article, only using one sentence of them, but the focus of the research be only on a few specific articles.
• A researcher can cite his or her previous research many times (self-citation) and this can influence his or her H-index and lead to a false result.
• Scientists and researchers who, for whatever reason, have had very low but very influential articles, receive little H-index (e.g. Albert Einstein, whose H-index is not high, but has heavily influenced the scientific world with those few articles!). The opposite is also true.
• As the values ​​of the h-index (i.e. citation and publication) increase over time, the h-index of a researcher depends on his/her scientific age, i.e. years of publication and activity, so young people should not be compared to older researchers by their h-index.
• Differences in citation rules in different scientific sectors are not considered in the h-index. It is believed that citation as a whole is influenced by factors related to the academic major of a researcher, which makes invalid the comparison of different academic areas and even different fields in the same major.