October 18, 2012: Modified SNIP
Leiden University's Centre for Science & Technology Studies (CWTS) has introduced a number of modifications to the SNIP journal metric.
The aim of these modifications is to further improve the mechanism used by the SNIP metric to correct for differences in citation practices between scientific fields. In this way, the accuracy of comparisons of the citation impact of journals from different fields will increase. The modifications that have been made only affect the denominator of the SNIP metric which is responsible for the correction for field citation pattern differences.
The three most significant modifications to SNIP:
- A different averaging procedure is used in the calculation of the denominator reducing the impact of outliers
- A correction factor is introduced to ensure that citations from journals with low numbers of references are weighted properly
- The new calculation results in a SNIP average score for all journals in Scopus to approximately equal one, making comparison of Journal scores easier
Created by Professor Henk Moed at CTWS, University of Leiden, Source-Normalized Impact per Paper (SNIP) measures contextual citation impact by weighting citations based on the total number of citations in a subject field. The impact of a single citation is given higher value in subject areas where citations are less likely, and vice versa.
It is defined as the ratio of a journal’s citation count per paper and the citation potential in its subject field. It aims to allow direct comparison of sources in different subject fields. Citation potential is shown to vary not only between journal subject categories – groupings of journals sharing a research field – or disciplines (e.g., journals in Mathematics, Engineering and Social Sciences tend to have lower values than titles in Life Sciences), but also between journals within the same subject category. For instance, basic journals tend to show higher citation potentials than applied or clinical journals, and journals covering emerging topics higher than periodicals in classical subjects or more general journals.
SNIP corrects for such differences. Its strengths and limitations are open to critical debate. All empirical results are derived from the Scopus abstract and indexing database. SNIP values are updated twice a year, providing an up-to-date view of the research landscape.
SNIP provides alternative values that bibliometricians can use to create more refined and objective analyses, including measuring the quality of the research output of universities (research performance) and helping governments and universities allocate research funding.
It helps editors evaluate their journal and understand how it is performing compared to its competition. SNIP provides more contextual information, and can give a better picture of specific fields, such as Engineering, Computer Science, and/or Social Sciences. It can also help all academics identify which journals are performing best within their subject field so they know where to publish. For more information, please see our FAQs.
Research Paper: "Measuring contextual citation impact of scientific journals"
This paper by Professor Henk Moed explores the methodology behind Source-Normalized Impact per Paper (SNIP).
- CWTS website
From this site, you can find SNIP values and related in-depth information about journals.