The number of citations of a scientific publication reflects its international resonance. Essential Science Indicators, a new database, contains the names of those scientists who are most frequently cited within a discipline (the top 1 %). This database was examined to identify the professors from 8 Swiss universities who belong to the top 1 %. According to the cumulative values of 10 disciplines of the life sciences the University of Zurich ranks first among the Swiss universities, and is followed by the Universities of Geneva, Lausanne and Basel. The University of Zurich has the top position in the category 'Neuroscience & Behavior' and 'Clinical Medicine', the University of Geneva in 'Molecular Biology & Genetics', the ETH Zurich in 'Engineering' and 'Environment/Ecology'. Taking into account not only the life sciences but the cumulative value of all disciplines, the ETH Zurich slightly exceeds the University of Zurich. In 'Chemistry' and 'Engineering' the ETH Zurich has the lead over the other universities. As is the case for all bibliographic analyses, also the present approach has its limitations and the results should not be used independently for ranking research at Swiss universities.

The publication of scientific results is an important part of research. It is a prerequisite for discussion and comments on an international level. The number of citations is an indicator of the impact of a publication in the international science community.

The bars in Fig. 1 reflect the extent of successful research in the life sciences. Focal areas of the different universities can be recognized. In Fig. 2 all research areas are represented. The strength of ETH Zurich in chemistry and environmental sciences is seen. The ordinate of the figures indicates the number of persons with citations in the top 1%.

Specific aspects of the analysis
The analysis is based on individuals rather than on institutions. Professors who were members of the faculty of a Swiss university at the time of the survey, were included irrespective of where they had spent the 10-year period of analysis. Only those faculties and departments were part of the analysis in which the research areas of the ESI database were represented¹⁾. For practical reasons, only professors were included and other scientists reaching the 1 % criterion were not considered. Since this procedure was applied for all universities, it is unlikely that a major bias was introduced.

The 1 % criterion is an arbitrary threshold. A different threshold may yield different results. Also the absolute number of citations are disregarded. Thus if at one university a few scientists have very high citations, while at another university a larger number of persons is just above threshold, the latter will have a more favorable outcome^2).

Citation analysis is not equally applicable to all areas of science. For example, important papers in certain branches of mathematics are published in conference proceedings rather than in journals. A similar situation prevails in 'Computer Science', 'Geosciences' and 'Engineering'. It is important to take into account such limitations when interpreting the results.

One of the assets of the ESI database is the reduction of the category 'Multidisciplinary'. Formerly, this category contained all publications in such renowned journals as Science, Nature and PNAS. Since these papers were not classified in a specific scientific category, a major bias was introduced. Universities publishing in these journals were penalized, because their highly cited papers did not appear in the specific field of science. The recent reclassification of a large part of the multidisciplinary journals has reduced this serious shortcoming.

1) Number of professors included in the survey:

University of Zurich:		242	Professors
ETH Zurich:		343	Professors
University of Basel:		185	Professors
University of Berne:		181	Professors
University of Fribourg:		64	Professors
University of Lausanne:		196	Professors
ETH Lausanne:		174	Professors
University of Geneva:		222	Professors

2) To assess the quality of publications, the 'number of citations per paper' is often used. The ESI database allows to extract this indicator for specific institutions and categories. Also according to this measure, the University of Zurich ranks first in the category 'Neuroscience & Behavior'. Moreover, it is in the top position also in 'Physics' and 'Immunology', a result that is not apparent from the present analysis.

	CEST-analysis The Center for Science and Technology Studies (CEST) published a report in August 2002 in which the Swiss universities were compared on the basis of bibliometric indicators. The results exhibit considerable discrepancies with regard to the present analysis as well as the analysis based on citations per paper. The origin of the discrepancies is unclear and requires detailed examination. The different databases could be one factor. The CEST analysis was based on the citations of 1994-99, whereas for the present analysis the 10-year ESI database (1992-2002) was used. A serious problem of the CEST analysis seems to be the use of the former category 'Multidisciplinary', which precludes a proper classification of highly cited papers. In this category, the University of Zurich holds the top positions, whereas in several specific categories it shows unexpected poor results. This may be due to the fact that some of the most important papers were not entered in their proper category.
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