Analyzing the activities of visitors of the Leiden Ranking website

The CWTS Leiden Ranking (www.leidenranking.com) provides bibliometric indicators for almost 1000 major universities worldwide. We present a detailed analysis of the activities of visitors of the Leiden Ranking website. We for instance study the countries from which visitors originate, the specific pages on the Leiden Ranking website that they visit, the countries or the universities that they find of special interest, and the indicators that they focus on. In addition, we also discuss two experiments that were carried out on the Leiden Ranking website. Our analysis aims to contribute to a better understanding of the way in which university rankings are used. We also intend to use the analysis to make improvements to the Leiden Ranking

A Theoretical Analysis of Cooperative Behavior in Multi-Agent Q-learning

A number of experimental studies have investigated whether cooperative behavior may emerge in multi-agent Q-learning. In some studies cooperative behavior did emerge, in others it did not. This report provides a theoretical analysis of this issue. The analysis focuses on multi-agent Q-learning in iterated prisoner’s dilemmas. It is shown that under certain assumptions cooperative behavior may emerge when multi-agent Q-learning is applied in an iterated prisoner’s dilemma. An important consequence of the analysis is that multi-agent Q-learning may result in non-Nash behavior. It is found experimentally that the theoretical results derived in this report are quite robust to violations of the underlying assumptions

The substantive and practical significance of citation impact differences between institutions: Guidelines for the analysis of percentiles using effect sizes and confidence intervals

In our chapter we address the statistical analysis of percentiles: How should the citation impact of institutions be compared? In educational and psychological testing, percentiles are already used widely as a standard to evaluate an individual's test scores - intelligence tests for example - by comparing them with the percentiles of a calibrated sample. Percentiles, or percentile rank classes, are also a very suitable method for bibliometrics to normalize citations of publications in terms of the subject category and the publication year and, unlike the mean-based indicators (the relative citation rates), percentiles are scarcely affected by skewed distributions of citations. The percentile of a certain publication provides information about the citation impact this publication has achieved in comparison to other similar publications in the same subject category and publication year. Analyses of percentiles, however, have not always been presented in the most effective and meaningful way. New APA guidelines (American Psychological Association, 2010) suggest a lesser emphasis on significance tests and a greater emphasis on the substantive and practical significance of findings. Drawing on work by Cumming (2012) we show how examinations of effect sizes (e.g. Cohen's d statistic) and confidence intervals can lead to a clear understanding of citation impact differences

Kwantitatieve geletterdheid voor verantwoord onderzoeksbeleid

Oratie uitgesproken door Prof.dr. Ludo Waltman bij de aanvaarding van het ambt van Hoogleraar Kwantitatief Wetenschapsonderzoek aan de Universiteit Leiden op vrijdag 21 juni 2019Merit, Expertise and Measuremen

A simple alternative to the h-index

The h-index is a popular bibliometric performance indicator. We discuss a fundamental problem of the h-index. We refer to this problem as the problem of inconsistency. There turns out to be a very simple bibliometric indicator that has similar properties as the h-index and that does not suffer from the inconsistency problem. We argue that the use of this indicator is preferable over the use of the h-index

VOSviewer: A Computer Program for Bibliometric Mapping

We present VOSviewer, a computer program that we have developed for constructing and viewing bibliometric maps. VOSviewer combines the VOS mapping technique and an advanced viewer into a single easy-to-use computer program that is freely available to the bibliometric research community. Our aim in this paper is to provide an overview of the functionality of VOSviewer and to elaborate on the technical implementation of specific parts of the program

Quantifying the long-term influence of scientific publications

We consider the long-term indirect influence of publications on subsequent publications. In particular, we are here interested in long-term scientific influence at the level of disciplines. We present a novel method to quantify the long-term scientific influence of publications, considering both direct and indirect, or higher-order citations. We apply this method to Web of Science data at the level of disciplines. Preliminary results for a specific operationalization of the notion of long-term scientific influence suggest that long-term influence is dominated by a few disciplines: Astronomy and Astrophysics, Basic Life Sciences, and Physics and Material Science.</p

Quantifying the long-term influence of scientific publications

We consider the long-term indirect influence of publications on subsequent publications. In particular, we are here interested in long-term scientific influence at the level of disciplines. We present a novel method to quantify the long-term scientific influence of publications, considering both direct and indirect, or higher-order citations. We apply this method to Web of Science data at the level of disciplines. Preliminary results for a specific operationalization of the notion of long-term scientific influence suggest that long-term influence is dominated by a few disciplines: Astronomy and Astrophysics, Basic Life Sciences, and Physics and Material Science.</p

Computational and Game-Theoretic Approaches for Modeling Bounded Rationality

This thesis studies various computational and game-theoretic approaches to economic modeling. Unlike traditional approaches to economic modeling, the approaches studied in this thesis do not rely on the assumption that economic agents behave in a fully rational way. Instead, economic agents are assumed to be boundedly rational. Abandoning the assumption of full rationality has a number of consequences for the way in which economic reality is being modeled. Traditionally, economic models are mostly of a static nature