Cited by 828scientometrics and bibliometrics researchWeb visibility and informetricsPsychology Research and Bibliometrics

The DOI matches its Crossref record; 35 of the 35 references it cites were found in a registry or an index; none of the 7 sources its claims cite is checked for support yet.

Universality of citation distributions: Toward an objective measure of scientific impact

Open access
Radicchi, Filippo, Fortunato, Santo, Castellano, Claudio·2008·Proceedings of the National Academy of Sciences

Abstract

We study the distributions of citations received by a single publication within several disciplines, spanning broad areas of science. We show that the probability that an article is cited c times has large variations between different disciplines, but all distributions are rescaled on a universal curve when the relative indicator c f = c / c 0 is considered, where c 0 is the average number of citations per article for the discipline. In addition we show that the same universal behavior occurs when citation distributions of articles published in the same field, but in different years, are compared. These findings provide a strong validation of c f as an unbiased indicator for citation performance across disciplines and years. Based on this indicator, we introduce a generalization of the h index suitable for comparing scientists working in different fields.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper shows that citation distributions across scientific disciplines and publication years collapse onto a universal curve when citations are rescaled by the field-year average \(c_0\), making \(c_f=c/c_0\) an unbiased relative indicator. It introduces a generalized h-index \(h_f\) based on \(c_f\) and normalized publication rates.

Key findings

  • Bare citation distributions vary strongly by discipline: a publication with 100 citations is approximately 50 times more common in Developmental Biology than in Engineering, Aerospace. After rescaling by \(c_0\), all distributions collapse onto a universal curve fitted by a lognormal with \(\sigma^2=1.3\).
  • Universality also holds across years within the same field: for Hematology, Neuroimaging, and Physics, Nuclear, articles from 1990, 1999, and 2004 show the same rescaled distribution despite \(c_0\) growing with elapsed time.
  • Ranking articles by \(c_f\) reduces field bias: for the top \(z=20\%\), the standard deviation of discipline bin heights is \(\sigma_z=1.15\%\) for \(c_f\)-based ranking versus \(12.37\%\) for bare \(c\), compared with the theoretical unbiased value \(\sigma_z=1.09\%\).
  • The generalized h-index \(h_f\) orders articles by \(c_f\) and uses reduced rank \(r/N_0\); an example with \(c_f\) values 4.1, 2.8, 2.2, 1.6, 0.8, 0.4 and \(N_0=2.0\) gives \(h_f=1.5\). Author publication counts also rescale, fitted by a power law with exponent \(-3.5(5)\).

Methods

  • Data come from Thomson Scientific’s Web of Science; journals are divided into 172 JCR categories, and only records classified as “article” and “letter” are considered. Citations are counted as the total number of times an article appears as a reference in a more recent published article.
  • For each discipline and year, the average citations per article \(c_0\) is computed; distributions \(P(c,c_0)\) are rescaled as \(c_0P(c,c_0)\) versus \(c_f=c/c_0\). Curves are fitted with a lognormal constrained by \(\sigma^2=-2\mu\) because the expected value of \(c_f\) is 1, using exponentially growing bins.
  • Ranking analysis pools disciplines, ranks articles by \(c\) and by \(c_f\), and compares the percentage of each discipline in the top \(z\%\) against an unbiased-ranking expectation. The generalized h-index is defined using \(c_f\) and \(r/N_0\).

Limitations

  • Stated: uncited articles are neglected, though the authors verified their inclusion only produces a small shift in \(c_0\); “Multidisciplinary sciences” does not fit perfectly because its citation distribution is a convolution of single disciplines, but restricting to Nature, Science, and PNAS fits well.
  • Stated: the analysis addresses single publications, not individuals or research groups, and other biases such as number of authors are left for future work; the origin of the universality is also not understood.
  • Evident from the text: JCR categories are not mutually exclusive, and the generalized h-index’s practical application is deferred to a forthcoming publication.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1073/pnas.0806977105

Cites

35 of 35 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

0 of 7 cited sources checked · 0 supported · 0 flagged

Show all 19 claims

  • It may state two separate claims as one. 5
  • Probably not a substantial claim. 1
5 of 5
  • The authors state this as an assumption.

    Under an unbiased ranking, articles of the various disciplines are scattered uniformly along the rank axis.

    “assuming that articles of the various disciplines are scattered uniformly along the rank axis, one would expect the average bin height in Fig. 3 to be z % with a standard deviation”
1 of 1

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Citations

Cites

Flagged first, then by citations

Show all 31 references

Cited by

Sorted by citations

Metadata

Authors
Radicchi, F., Fortunato, S., & Castellano, C.
Affiliations
  • Institute for Scientific Interchange (IT)
  • National Research Council (IT)
Corresponding author
Castellano, Claudio
Venue
Proceedings of the National Academy of Sciences
Published
2008-11-11
Volume
105
Issue
45
Pages
17268-17272
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
OpenAlex
W2151866568
Cited by
828
References
31
Citations by year
2026: 20 · 2025: 38 · 2024: 42 · 2023: 40 · 2022: 41 · 2021: 48 · 2020: 53 · 2019: 64 · 2018: 44 · 2017: 75 · 2016: 58 · 2015: 56 · 2014: 57 · 2013: 61 · 2012: 48
FWCI
31.18
Type
journal article
Language
en
Open access
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Social Sciences › Library and Information Sciences › scientometrics and bibliometrics research
  • Physical Sciences › Computer Science › Information Systems › Web visibility and informetrics
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Psychology Research and Bibliometrics
Keywords
citation distribution, scientific impact, h-index, cross-disciplinary comparison, rescaling, citation performance, bibliometric analysis
MeSH terms
Models, Theoretical, Selection Bias, Interdisciplinary Communication, Journal Impact Factor

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

A language model drew the claims from the paper on 2026-10-06, under version 3 of the claim definition (model deepseek-v4.1-flash, prompt extract-v3).

A second model labelled each claim on 2026-10-06 (model jev-1.13-20260917, definition revision gold-guideline-v0.2).

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review