Source normalized indicators of citation impact: an overview of different approaches and an empirical comparison
- 992 Downloads
Different scientific fields have different citation practices. Citation-based bibliometric indicators need to normalize for such differences between fields in order to allow for meaningful between-field comparisons of citation impact. Traditionally, normalization for field differences has usually been done based on a field classification system. In this approach, each publication belongs to one or more fields and the citation impact of a publication is calculated relative to the other publications in the same field. Recently, the idea of source normalization was introduced, which offers an alternative approach to normalize for field differences. In this approach, normalization is done by looking at the referencing behavior of citing publications or citing journals. In this paper, we provide an overview of a number of source normalization approaches and we empirically compare these approaches with a traditional normalization approach based on a field classification system. We also pay attention to the issue of the selection of the journals to be included in a normalization for field differences. Our analysis indicates a number of problems of the traditional classification-system-based normalization approach, suggesting that source normalization approaches may yield more accurate results.
KeywordsBibliometric indicator Citation analysis Field normalization Source normalization
We would like to thank Javier Ruiz Castillo for his comments on an earlier draft of this paper. We are also grateful to an anonymous referee for various useful comments.
- Glänzel, W., Thijs, B., Schubert, A., & Debackere, K. (2009). Subfield-specific normalized relative indicators and a new generation of relational charts: methodological foundations illustrated on the assessment of institutional research performance. Scientometrics, 78(1), 165–188.CrossRefGoogle Scholar
- Leydesdorff, L., Zhou, P., & Bornmann, L. (in press). How can journal impact factors be normalized across fields of science? An assessment in terms of percentile ranks and fractional counts. J Am Soc Inf Sci Technol.Google Scholar
- Crespo, J. A., Li, Y., & Ruiz-Castillo, J. (2012). Differences in citation impact across scientific fields (Working Paper Economic Series 12-06). Departamento de Economía, Universidad Carlos III of Madrid.Google Scholar
- Van Eck, N. J., Waltman, L., Van Raan, A. F. J., Klautz, R. J. M., & Peul, W. C. (2012). Citation analysis may severely underestimate the impact of clinical research as compared to basic research. arXiv:1210.0442.Google Scholar
- Waltman, L., & Van Eck, N. J. (2010a). A general source normalized approach to bibliometric research performance assessment. In Book of Abstracts of the Eleventh International Conference on Science and Technology Indicators (pp. 298–299).Google Scholar
- Waltman, L., & Van Eck, N. J. (in press). A new methodology for constructing a publication-level classification system of science. J Am Soc Inf Sci Technol. Google Scholar
- Waltman, L., Van Eck, N. J., Van Leeuwen, T. N., & Visser, M. S. (2012). Some modifications to the SNIP journal impact indicator. arXiv:1209.0785.Google Scholar