Source Normalized Impact per Paper (SNIP)
Also known as: SNIP, Citation Potential Normalization, Source-Normalized Journal Impact, Field-Normalized Citations per Paper
The Source Normalized Impact per Paper, or SNIP, corrects a journal's citation rate for the citation behavior of its field so that journals in heavily cited and lightly cited disciplines can be compared on the same scale. Henk Moed introduced SNIP in 2010 with a distinctive twist: rather than classifying journals into predefined subject categories, it defines a journal's field from the bottom up as the set of papers that actually cite it, and it normalizes by that field's citation potential, measured from how long the citing papers' reference lists are. Fields whose authors cite many references generate more citations to go around, so a raw citation rate means different things in mathematics than in molecular biology. SNIP divides raw impact per paper by this citation potential to produce a field-corrected indicator. Ludo Waltman and colleagues revised the original formula in 2013 to remove some counterintuitive properties and improve stability; the revised SNIP is the version distributed in Scopus.
Key highlights
- Normalizes for differences in citation density and speed between fields, enabling fair cross-disciplinary journal comparison.
- Defines a journal's field empirically from its citing papers, adapting well to interdisciplinary and emerging journals.
- Uses a three-year window better suited to slow-citing fields than the two-year impact factor.
- The revised 2013 formulation removes counterintuitive properties and is stable enough for routine evaluation.
Intuition
This section is available to Pro members. Upgrade to Pro
How it works
This section is available to Pro members. Upgrade to Pro
When to use it
Use SNIP when you need to compare the citation impact of journals across fields with very different citation densities and speeds, and you want a normalization that adapts to a journal's actual citing audience rather than relying on fixed subject categories. It is well suited to interdisciplinary journals and to evaluation exercises that span heterogeneous disciplines, where a raw impact factor would systematically favor high-citing fields. SNIP requires good coverage of reference lists in the source database, so it is most reliable in fields well indexed by Scopus. It is less appropriate where reference-list data are sparse or unreliable, for very small or very new journals whose citing field is thin, and for evaluating individual papers or authors, since it is a journal-level indicator. It pairs naturally with SJR and Eigenfactor metrics, which normalize on the cited rather than the citing side.
Strengths & limitations
- Normalizes for differences in citation density and speed between fields, enabling fair cross-disciplinary journal comparison.
- Defines a journal's field empirically from its citing papers, adapting well to interdisciplinary and emerging journals.
- Uses a three-year window better suited to slow-citing fields than the two-year impact factor.
- The revised 2013 formulation removes counterintuitive properties and is stable enough for routine evaluation.
- Depends on accurate reference-list data, so it is only as reliable as the source database's coverage of references.
- The citing-side field definition can be unstable for journals with few citing papers in a given year.
- Citation potential is sensitive to how 'active' or recent references are delimited, a choice that affects scores.
- As a journal-level metric it must not be used to assess individual articles or researchers.
Common pitfalls
This section is available to Pro members. Upgrade to Pro
Applications
This section is available to Pro members. Upgrade to Pro
Frequently asked
What makes SNIP 'source normalized'?
The normalization comes from the citing source's behavior. SNIP defines a journal's field as the papers that cite it and measures that field's citation potential from how many recent references those citing papers make. Because fields that cite more references generate more citations to go around, SNIP divides a journal's raw citations per paper by this citation potential. The correction is applied on the source (citing) side, which is why it is called source normalized, in contrast to metrics that normalize using predefined cited-side subject categories.
How does SNIP differ from the impact factor?
The impact factor is raw citations per paper over a two-year window with no correction for field. SNIP uses a three-year window and then divides the raw rate by the citation potential of the journal's empirically defined field, so it corrects for the fact that some fields cite more and faster than others. A SNIP of one means a journal performs about as its field would predict, making SNIP comparable across disciplines in a way the impact factor is not.
Should I use the original or the revised SNIP?
Use the revised SNIP. Waltman and colleagues showed in 2013 that Moed's original formula had counterintuitive properties, such as scores changing in unexpected ways when journals are split or merged. Their revised version recomputes the citation-potential normalization at the level of individual citing papers and uses a stabilized averaging that removes these anomalies while preserving the core source-normalization idea. Elsevier replaced the original with the revised SNIP in Scopus, so the values you encounter today are the revised ones.
Sources
- 1.Moed, H. F. (2010). Measuring contextual citation impact of scientific journals. Journal of Informetrics, 4(3), 265-277.
- 2.Waltman, L., van Eck, N. J., van Leeuwen, T. N., & Visser, M. S. (2013). Some modifications to the SNIP journal impact indicator. Journal of Informetrics, 7(2), 272-285.
You have read it. What now?
Cite this page
ScholarGate. (2026, June 23). Source Normalized Impact per Paper (SNIP). ScholarGate. https://scholargate.app/bibliometrics/source-normalized-impact-per-paper