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Impact Factors and Citation Analysis: Researcher Impact

Adapted from Impact Factors and Citation Analysis, Robert W. Woodruff Library, Emory University; used by permission.


Your productivity as a researcher can be measured by your total number of articles, and the impact of your research can be measured by the total number of times your articles have been cited. The h-index (AKA Hirsch index) is a combined measure of both productivity and impact. An index of h means that your h most highly-cited articles have at least h citations each. 

The h-index is more informative than total number of articles (which ignores how well those articles have been received by other researchers) or total number of citations (which can be inordinately influenced by a small number of highly-cited articles and therefore not an accurate reflection of productivity). 

One caveat about the h-index is that it correlates with the length of a researcher's career (i.e., researchers who have been publishing for longer tend to have higher h-indices). It can also be inflated by self-citation. In addition, the h-index ignores the order of authorship, which is very important in some disciplines. Additionally, because different disciplines have different publishing practices, the h-index should not be used to compare researchers across different disciplines. Average impact scores vary widely from discipline to discipline.

Alternative indices

Some claim that average number of citations per article or total number of citations is just as good a measure asif not better thanthe h-index. 

One of the strengths of the h-index—its insensitivity to highly-cited papers—could also be considered a weakness. That is, once an article has a sufficient number of citations to gain inclusion into the h core, additional citations are irrelevant. The g-index, in contrast, weights highly-cited papers more heavily. An index of g means that your most highly-cited articles together have at least g-squared citations. Your g-index will always be equal to or greater than your h-index.

If multiple-authored articles are common within your discipline, your h-index may be relatively high. Your degree of contribution to each article, however, may be thought to diminish as your number of co-authors increases. The hi-index (AKA individual h-index) takes number of co-authors into account. Your hi-index is equal to your h-index divided by the average number of authors on the articles in your h core. 

If you published a few highly-cited papers decades ago but are now inactive, your h-index may be higher than an established researcher who steadily continues to publish or a promising new researcher who is just beginning to gain recognition. The hc-index (AKA contemporary h-index) weights newer articles more heavily than older articles, so that articles lose their value over time. This allows a clearer picture of more recent levels of productivity and impact. 

If your have been publishing for decades, your h-index will be higher than a researcher who has been publishing for only a few years. The m-index takes differences in career length into account, by dividing your h-index by the number of years that you have been publishing. 

Several other alternative indices have also been proposed. 

Unique researcher IDs

Due to common researcher names, name changes, cultural differences in name order, and inconsistent use of middle initials, it can be difficult to accurately calculate measures of personal impact. Numeric codes can help identify individual researchers. 

ORCID (Open Researcher and Contributor ID)

ResearcherID (Thomson Reuters)

By registering for a unique identifier, you can potentially connect a diverse array of your scholarly output, including journal articles, datasets, patents, and online comments.

Tools for calculating h-index

Google ScholarTo calculate your h-index and see trends in your impact across time, create a public or private profile. Unlike other databases, Google Scholar provides citation information not only for journal articles but also for conference papers and books.  

Publish or PerishDownload this free software, which uses information from Google Scholar to calculate h-index and several h-index alternatives. A companion user's guide, The Publish or Perish Book, is available in the Emory book stacks. 

Scholarometer: Install this browser (Firefox or Chrome) extension and search for an author to receive a list of articles, number of citations, h-index, and h-index alternatives based on information from Google Scholar.

Web of Science: Search for an author, then click Create Citation Analysis to calculate h-index and see trends in impact across time. 

Microsoft Academic Search: Search for an author to calculate h-index and see trends in impact across time. 

h-index Prediction Tool: Predict what your h-index will be in the future.

NOTE: As these tools use different ways of searching for articles and citations, they tend to provide differing results. 


Calculating h-index using Web of Science

Calculating h-index using Google Scholar