What is the h-index used for and how is it calculated?
A researcher has index h if h of his/her publications have at least h citations each. This means that a researcher with an h-index of 20, has 20 publications that have been cited at least 20 times each
Read more about the calculation of h-index, and some critical remarks, on Phd on Track.
The h-index is widely used because it is easy to calculate and has the advantage of describing both publishing activity (number of publications) and impact (number of citations).
The h-index is not suitable for comparing researchers across disciplines because of the large difference not only in how they publish, but also when and how they cite research.
Because the h-index depends on the data source, i.e. the journals and other material indexed by the database used to calculate the h-index, the individual researcher's h-index will depend on whether it is calculated in Google Scholar, Web of Science or Scopus.
The index favours older rather than younger researchers. It is not sensitive to very highly cited publications.
The h-index does not assess the quality of your publications. For instance, negative citations may increase an author’s h-index. As in the case of other bibliometric indicators it is vulnerable to mistakes and manipulations, and it is also influenced by the systematic skewing of citations known as the Matthew effect in science: Articles that are already widely cited, are likely to receive even more citations.