Despite some limitations, the number of citations is one of the accepted measures of the impact of an article. A high number of citations is associated with a greater impact.
It is often useful for a researcher to highlight the number of citations received by their articles in order to demonstrate the impact that they have had in their field.
Citation practices vary greatly from one field to another: an article in biology will on average be much more cited than an article in mathematics. One cannot therefore compare the impact of two articles in two different fields on the basis of the absolute number of citations received.
Access the citations databases
Several databases make it possible to find the citations received by an article:
The h-index is a measure developed by J. E. Hirsch in 2005. It is a unique indicator that takes into account a researcher's productivity (number of articles published) and impact (number of citations received). The h-index is the "n" number of publications that have been cited at least "n" times.
Like all indicators, the h-index has certain limitations:
It varies greatly between subject areas, so it should not be used to compare researchers from different fields;
It varies greatly depending on the researcher's age and career length;
It does not take into account the author order and the number of authors an article has;
The the h-index ignores excess citations (an author who has published a single paper with 300 citations will still have an h-index of 1).
The Library has developed a tutorial outlining the steps to find an h-index in Web of Science.
Google Scholar can also be used to find an h-index. However, an expert panel commissioned by the Council of Canadian Academies has stated that "Google Scholar should not be used as a data source for rigorous bibliometric assessment" (Source: Informing Research Choices: Indicators and Judgment, 2012, pp. 60).
To manually find an h-index, list the articles in descending order of citations received and find the point when the rank of the article is higher than the number of citations. The h-index will be the previous rank. In the example below, the h-index is 7.
Figure 1: h-Index calculated from a decreasing number of citations, 2008. In the public domain.
Fractional counting can be used to count an author's publications. This algorithm counts each article as 1 ÷ (number of authors). Fractional counting can also be used for citations.
It may also be relevant to assess the number or the percentage of articles that an author has written collaboratively. This collaboration may be inter-institutional, international or cross-sectoral. The Analyze Results tool in Web of Science is one means to assess collaboration.
The Relative Citation Ratio (RCR) compares the citations received by an article to the average number of citations an article usually receives in that field. This indicator can be used for citations received by a particular article, although it is often used to compare the average of all citations received by an author, institution or even a country with the world average. The RCR is more appropriate for comparing researchers in different fields.
Several researchers have developed indicators to complement the h-index. The best known are the g-index and the e-index, which provide information on citations that exceed the h-index. It has also been suggested to calculate the h-index over 5 years, which would make it easier to compare researchers who are not at the same point in their careers.
Also, the altmetrics are increasingly used to measure impact.