The H-index is a formula developed by Jorge Hirsch in 2005 designed to measure a research author's contribution to a field of study. The H-index is based on the researcher's highly cited publications. An H-index of 20 indicates 20 of an author's publications have been cited 20 or more times by other researchers. H-index scores are also used to evaluate research institutions programs of study. (Cooper, 2015)
Web of Science and Google Scholar calculate the H-index for an author's set of articles.