Field-Normalized Citation Impact (MNCS)
Also known as: Mean Normalized Citation Score, MNCS, normalized citation impact, new crown indicator
The Mean Normalized Citation Score (MNCS) is the field-normalized citation impact indicator developed at the Centre for Science and Technology Studies (CWTS) in Leiden and articulated in Waltman and colleagues' 2011 paper on a new crown indicator. Raw citation counts cannot be compared across fields, because a molecular biology paper and a mathematics paper accumulate citations at vastly different rates, and older papers have had more time to be cited. The MNCS removes these distortions by dividing each paper's citations by the average citations of comparable papers in the same field, document type, and publication year, then averaging these normalized ratios. A value of 1 means performance exactly at the world average for the relevant fields, while values above or below 1 indicate above- or below-average impact.
Key highlights
- Makes citation impact comparable across fields, document types, and publication years by benchmarking each paper against its peers.
- Anchored at an interpretable world-average value of 1, so deviations are easy to read.
- Averages normalized ratios rather than ratios of sums, giving each publication equal weight and better statistical behavior.
- Serves as the established standard for institutional and national research evaluation, including the Leiden Ranking.
Intuition
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How it works
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When to use it
Use field-normalized citation impact whenever you must compare the citation performance of researchers, groups, institutions, or countries that work in different fields or whose outputs span different years, since raw counts and even the h-index are confounded by field and age. The MNCS is the standard indicator for research evaluation and university rankings such as the Leiden Ranking. It requires a citation database with a defensible field classification and reliable document-type and year metadata. It is less suitable for very small publication sets, where a single highly cited paper dominates the average, and it depends heavily on the chosen field-delineation scheme, which should be stated and justified.
Strengths & limitations
- Makes citation impact comparable across fields, document types, and publication years by benchmarking each paper against its peers.
- Anchored at an interpretable world-average value of 1, so deviations are easy to read.
- Averages normalized ratios rather than ratios of sums, giving each publication equal weight and better statistical behavior.
- Serves as the established standard for institutional and national research evaluation, including the Leiden Ranking.
- Highly sensitive to the field-classification scheme used to define reference sets, with no single agreed standard.
- Unstable for small publication sets, where one extreme paper can dominate the mean of ratios.
- Depends on a citation database with accurate, comprehensive field, document-type, and year metadata.
- Cannot fully resolve interdisciplinary papers that straddle multiple fields with different citation norms.
Common pitfalls
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Applications
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Frequently asked
What does an MNCS value mean?
The MNCS expresses citation impact relative to the world average for comparable papers. A value of 1 means the publications were cited exactly as often as the average paper of the same field, document type, and year. A value of 2 means twice the field-and-year average, and 0.5 means half. Because it is normalized, an MNCS can be compared fairly across fields and across time, unlike raw citation counts.
How does the MNCS differ from the old CPP/FCSm crown indicator?
The original CWTS crown indicator computed a ratio of total citations to total expected citations, effectively a ratio of averages. Waltman and colleagues showed in 2011 that this approach let high-citation fields dominate the result and had inconsistent properties. The MNCS instead averages the per-paper normalized scores, an average of ratios, which gives each publication equal weight and behaves better statistically. This is why the MNCS is called the new crown indicator.
Why is the choice of field classification so important?
The MNCS benchmarks each paper against others in its field, so the way fields are delineated directly shapes the expected citation counts and therefore the normalized scores. Classifications that are too broad mix dissimilar specialties, while overly narrow ones create unstable reference sets. Because there is no universally agreed scheme, the classification used should always be disclosed, and MNCS values computed under different schemes or databases should not be compared as if identical.
Sources
- 1.Waltman, L., van Eck, N. J., van Leeuwen, T. N., Visser, M. S., & van Raan, A. F. J. (2011). Towards a new crown indicator: Some theoretical considerations. Journal of Informetrics, 5(1), 37-47.
- 2.Moed, H. F., De Bruin, R. E., & Van Leeuwen, T. N. (1995). New bibliometric tools for the assessment of national research performance: Database description, overview of indicators and first applications. Scientometrics, 33(3), 381-422.
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Cite this page
ScholarGate. (2026, June 23). Field-Normalized Citation Impact (MNCS). ScholarGate. https://scholargate.app/bibliometrics/field-normalized-citation-impact