The e-index, complementing the h-index for excess citations

PLoS One. 2009;4(5):e5429. doi: 10.1371/journal.pone.0005429. Epub 2009 May 5.


Background: The h-index has already been used by major citation databases to evaluate the academic performance of individual scientists. Although effective and simple, the h-index suffers from some drawbacks that limit its use in accurately and fairly comparing the scientific output of different researchers. These drawbacks include information loss and low resolution: the former refers to the fact that in addition to h(2) citations for papers in the h-core, excess citations are completely ignored, whereas the latter means that it is common for a group of researchers to have an identical h-index.

Methodology/principal findings: To solve these problems, I here propose the e-index, where e(2) represents the ignored excess citations, in addition to the h(2) citations for h-core papers. Citation information can be completely depicted by using the h-index together with the e-index, which are independent of each other. Some other h-type indices, such as a and R, are h-dependent, have information redundancy with h, and therefore, when used together with h, mask the real differences in excess citations of different researchers.

Conclusions/significance: Although simple, the e-index is a necessary h-index complement, especially for evaluating highly cited scientists or for precisely comparing the scientific output of a group of scientists having an identical h-index.

MeSH terms

  • Abstracting and Indexing
  • Bibliometrics
  • Research Personnel*