Hirsch-index The h-index was invented in August 2005 by Jorge E. Hirsch, a physicist at the University of California (San Diego) and it is a simple measure of citation.  A researcher’s Hirsch-index is h, if there are h articles that have at least h references to each. Therefore, if a researcher’s h-(Hirsch-) index is 21, then he/she has 21 publications to which at least 21 citations have been made separately.