The article "Caveats for the journal and field normalizations in the CWTS (`Leiden') evaluations of research performance", published by Tobias Opthof and Loet Leydesdorff (arXiv:1002.2769) deals with a subject as important as the application of so called field normalized indicators of citation impact in the assessment of research performance of individual researchers and research groups. Field normalization aims to account for differences in citation practices across scientific-scholarly subject fields. As the primary author of the papers presenting the "Leiden" indicators and of many reports and articles reporting on the outcomes of assessments actually using these measures, I comment on the 3 main issues addressed in the paper by Opthof and Leydesdorff.

翻译：由Tobias Opthof和Loet Leydesdorf(arXiv:1002.2769)出版的文章“CWTS(`利登')研究业绩评价的期刊和实地正常化”涉及一个与在评估个别研究人员和研究团体的研究业绩时应用所谓的实地引用影响标准化指标同样重要的主题。实地正常化的目的是说明科学学科领域在引用做法方面的差异。作为介绍“利登”指标以及报告实际使用这些措施的评估结果的许多报告和文章的主要作者,我评论了Opthof和Leydesdordf在论文中提到的三个主要问题。