Measuring Research Impact: Citations and indicators

Metrics Methods and Evaluation

Citations and citation analysis

Citation analysis examines the impact of a publication, an author or an institution, based on the number of times works and/or authors have been cited by others.


  • Citations of a publication reveal the attention it has received rather than indicate its quality.
  • Citations are a researcher's subjective choice, which can be affected by many factors, e.g.age, language or easy availability of a publication.
  • Different citations in a paper are usually unequally important - the cited reference is either marginally or highly related to the article citing it.
  • Different citations usually come from papers with different influence and quality.
  • Document age and discipline influence the number of citations it has, or is likely to receive.

The citation data will relate only to articles indexed within the database. Variation may occur because the databases:

  • Index different publication sources
  • Cover different date ranges
  • Include poor-quality data (duplicate records, misspelt citations etc)

Read more: Citation analysis and databases containing citation information / Oulu University Library

Other indicators

The g-index weights highly-cited papers more heavily. An index of g means that your g 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.
Egghe, L. (2006). Theory and practise of the g-index. Scientometrics, 69(1), 131-152.

Contemporary h-index (hc-index)
The hc-index adds an age-related weighting to each cited article, giving less weight to older articles.
It gives more weight to recent and highly cited research than to older research, although maybe being highly cited.

Sidiropoulos, A., Katsaros, D., Manolopoulos, Y. (2006). Generalized h-index for Disclosing Latent Facts in Citation Networks.


Author's h-index means that
an author has published h papers each of which has been cited (by others) at least h times.

The value of h-index is affected by scientific field (different publishing and citation practices), length of researcher's career (longer time-window enables more publications and citations) and by total number of publications (h-index can't be larger than number of publications).

Author's h-index can be found in Web of Science (instructions), Scopus or Google Scholar.

More information:

University of Oulu: Evaluation based on scientific publishing-guide: h-index
Wikipedia: h-index
Hirsch, J. E. (2005). An index to quantify an individual's scientific research output,

Normalized citation indicators – citation counts put in context

Normalized indicators show how a publication or group of publications performs relative to averages or baselines. The citation count of a publication is normalized by an average citation count through controlling research field, document type and publishing year, so that comparing sets of publications like research outputs of Universities would be meaningful. Even though basic idea is the same, different data providers name and count normalized indicators somewhat differently:

Top%- indicators - percentage of documents in top x% most frequently cited

The number or the proportion of researchers/groups/organizations publications that, compared with other publications in the same field and in the same year, belong to the top x % most frequently cited. Even though basic idea is the same, different data providers name and count normalized indicators somewhat differently: