Many indices have been developed to provide a simple score to assess a researcher's productivity and impact. The most widely used in the h-index, presented by Hirsch, J. E. (2005). An index to quantify an individual's scientific research output. Proceedings of the National academy of Sciences of the United States of America, 102(46), 16569-16572.

The h-index considers a researcher's productivity, in terms of number of publications, and his/her impact, in terms of citation counts. A researcher's impact is h when s/he has h articles cited at least h times. Example: an author's h-index is 7. This means that they've published 7 papers that have been cited at least 7 times each.

While the h-index can be an effective method to measure citations and research impact, it is important to remember its limitations:

• The h-index depends upon the discipline of research. H-indices tend to be higher within the sciences where researchers publish more frequently and use many references, while h-indices are lower in social sciences, arts, and humanities, where researchers tend to publish fewer papers that are longer in length.
• High-interest topics often lead to high h-indices
• Papers in English receive more citations than publications in other languages, which means that researchers who publish in English will likely have a higher h-index.
• Authors who often publish as a part of large groups tend to have higher h-indices. Hirsch argues that “this creates an incentive for authors to form collaborations that are not scientifically well justified” (2014, p.162)

Hirsch reminds us that

the h-index should never be used as the only factor to evaluate a researcher (2014, p.163)

Limitations have been collated from: Hirsch, J.E. & Buela-Casal, G. (2014). The meaning of the h-index. International Journal of clinical and Health Psychology. 14(2), p.161-164.