What is a citation? Citations and the h-index explained simply
Every research paper builds on earlier work, and it shows this by citing it. Counting those citations has become one of the most common ways to measure a paper's or a scientist's influence.
What is a citation?
A citation is a reference in one paper to another paper. When a new study says "as shown by Smith et al. (2020)" and lists that paper in its references, Smith's paper gains one citation.
Each day, new papers add hundreds of thousands of citations to older work. ResearchBoard counts them as "citations made" on the live dashboard.
Why do citations matter?
- For papers: a highly cited paper is one that many other researchers found useful — often a new method, a large dataset, or an important discovery.
- For scientists: hiring and funding committees often look at citation numbers, alongside many other factors.
- For readers: citation counts help you find the important papers in a field quickly.
See which papers have the most citations in our list of the most-cited research papers, and which researchers lead in the most-cited scientists in the world.
What is the h-index?
The h-index was proposed by physicist Jorge Hirsch in 2005. It combines how many papers a researcher has published with how often they are cited, in a single number.
A scientist has an h-index of h if h of their papers have each been cited at least h times.
An example
A researcher has six papers with these citation counts, sorted from highest to lowest:
| Paper | Citations | At least this many citations? |
|---|---|---|
| 1st | 25 | 25 ≥ 1 ✓ |
| 2nd | 12 | 12 ≥ 2 ✓ |
| 3rd | 8 | 8 ≥ 3 ✓ |
| 4th | 5 | 5 ≥ 4 ✓ |
| 5th | 3 | 3 ≥ 5 ✗ |
| 6th | 1 | 1 ≥ 6 ✗ |
Four papers have at least four citations each, so the h-index is 4. Publishing many rarely cited papers does not raise it, and neither does one single famous paper.
What citation numbers cannot tell you
- Fields differ. Biomedicine and computer science cite far more than mathematics or the humanities, so compare scientists only within the same field.
- Time matters. Older papers have had longer to collect citations; a brilliant new paper may have very few so far.
- Citations are not always praise. A paper can be cited because others disagree with it or found an error.
- Databases differ. Google Scholar, Scopus, Web of Science and OpenAlex each count slightly different sets of papers, so the same person can have different numbers in each.
Use citation counts as one clue among many — never as the only measure of good science.
Explore citations every day
ResearchBoard tracks which papers and scientists gain the most citations each day. See the papers and scientists pages.