h-index
Publishing & metrics
A metric of an author's productivity and impact: the largest number h such that h of their papers each have at least h citations.
The h-index summarises a researcher's output and impact in one number: an h-index of 12 means the author has 12 publications that have each been cited at least 12 times. It rewards sustained, consistently cited output rather than a single highly cited paper or a long list of uncited ones.
Its value differs by source, because Google Scholar, Scopus and Web of Science index different bodies of literature — Google Scholar figures are typically the highest since it counts theses, preprints and book chapters. Always state which database an h-index came from.
The main limitations are that it rises with career length, so early-career researchers are structurally disadvantaged, that it varies hugely between disciplines and cannot be compared across them, and that it never decreases. Variants such as the i10-index, g-index and field-normalised measures address parts of this, but no single number captures research quality.
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