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