Research Impact: Citation Indexes

What are index numbers?

Citation index numbers provide a way to measure impact beyond raw citation counts. Index numbers can be calculated for individual articles, a group/list of publications, or even all the articles published in a journal or field (see our Journal Impact page).

What is the "best" index number?

Generally, the "best" measurement depends on what matters to you. The h-index is the most widely known index measurement. Some alternative measurements, like the g-index, address specific issues with the h-index. Other measurements target recent publications and citations, such as the the contemporary h-index. 

Alternatives to the h-index include:

• g-index: Gives more weight to highly cited publications. The original h-index is insensitive to high "outliers" -- a few papers that have very high citation counts will not sway the h-index score (much). The g-index allows highly cited papers to play a larger role in the index, and tends to emphasize visibility and "lifetime achievement."
• hc-index (contemporary h-index): Gives more weight to recent publications. The original h-index favors senior researchers with extensive publication records, even if they have ceased publishing. The hc-index attempts to correct this and favors researchers currently publishing.
• i10-index: Measures the number of papers that have at least 10 citations. Introduced (and used) by Google Scholar.
• m-quotient: Divides the h-index by the number of years since the researcher's first published paper. m-quotient was proposed as a way to help younger researchers who may not have long publication lists.

For more index measurements, we suggest "Reflections on the h-index," by Prof. Anne-Wil Harzing, University of Melbourne.

What is the h-index?

The h-index attempts to correlate a researcher's total publications and total citations. It was proposed by Jorge E. Hirsch in 2005 ("An index to quantify an individual's scientific research output," PNAS November 15, 2005 vol. 102 no. 46 16569-16572). For more information, see the Wikipedia article.

How do I calculate my h-index?

• Web of Science or Google Scholar will automatically calculate the h-index for the list of publications in your profile. 
• Publish or Perish will calculate h-index (and many other index numbers) for an author's publications. 
• If you want to calculate an h-index manually, Hirsch defines the h-index as follows: "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."