University of Mannheim

About: University of Mannheim is a education organization based out in Mannheim, Germany. It is known for research contribution in the topics: Context (language use) & Politics. The organization has 4448 authors who have published 12918 publications receiving 446557 citations. The organization is also known as: Uni Mannheim & UMA.

The Graph Structure in the Web – Analyzed on Different Aggregation Levels

Abstract: Knowledge about the general graph structure of theWorldWideWeb is important for understanding the social mechanisms that govern its growth, for designing ranking methods, for devising better crawling algorithms, and for creating accurate models of its structure. In this paper, we analyze a large web graph. The graph was extracted from a large publicly accessible web crawl that was gathered by the Common Crawl Foundation in 2012. The graph covers over 3:5 billion web pages and 128:7 billion hyperlinks. We analyze and compare, among other features, degree distributions, connectivity, average distances, and the structure of weakly/strongly connected components. We conduct our analysis on three different levels of aggregation: page, host, and pay-level domain (PLD) (one “dot level” above public suffixes). Our analysis shows that, as evidenced by previous research (Serrano et al., 2007), some of the features previously observed by Broder et al., 2000 are very dependent on artifacts of the crawling process, whereas other appear to be more structural. We confirm the existence of a giant strongly connected component; we however find, as observed by other researchers (Donato et al., 2005; Boldi et al., 2002; Baeza-Yates and Poblete, 2003), very different proportions of nodes that can reach or that can be reached from the giant component, suggesting that the “bow-tie structure” as described by Broder et al. is strongly dependent on the crawling process, and to the best of our current knowledge is not a structural property of the Web. More importantly, statistical testing and visual inspection of size-rank plots show that the distributions of indegree, outdegree and sizes of strongly connected components of the page and host graph are not power laws, contrarily to what was previously reported for much smaller crawls, although they might be heavy tailed. If we aggregate at pay-level domain, however, a power law emerges. We also provide for the first time accurate measurement of distance-based features, using recently introduced algorithms that scale to the size of our crawl (Boldi and Vigna, 2013).

Recovery rates of commercial lending: Empirical evidence for German companies

Abstract: There are very few studies concerning the recovery rate of bank loans. Prediction models of recovery rates are increasing in importance because of the Basel II-framework, the impact on credit risk management, and the calculation of loan rates. In this study, we focus the analyses on the distribution of recovery rates and the impact of the quota of collateral, the creditworthiness of the borrower, the size of the company and the intensity of the client relationship on the recovery rate. All our hypotheses can be confirmed. A higher quota of collateral leads to a higher recovery rate, whereas the risk premium of the borrower and the size of the company is negatively related to the recovery rate. Borrowers with an intense client relationship with the bank exhibit a higher recovery rate.

A review of conceptual approaches and empirical evidence on probability and nonprobability sample survey research

Abstract: There is an ongoing debate in the survey research literature about whether and when probability and nonprobability sample surveys produce accurate estimates of a larger population. Statistical theory provides a justification for confidence in probability sampling as a function of the survey design, whereas inferences based on nonprobability sampling are entirely dependent on models for validity. This article reviews the current debate about probability and nonprobability sample surveys. We describe the conditions under which nonprobability sample surveys may provide accurate results in theory and discuss empirical evidence on which types of samples produce the highest accuracy in practice. From these theoretical and empirical considerations, we derive best-practice recommendations and outline paths for future research.

Supporting Democracy: Political Participation and Political Attitudes. Exploring Causality Using Panel Data

Abstract: The relationship between political participation and political attitudes is at the heart of any discussion about fostering democratic engagement. However, many authors simply presume that political attitudes reinforce political behaviour. Using a three-wave panel data set with more than 3,000 adolescents, we show that political attitudes do not necessarily precede behaviour. On the contrary, focusing on the relationships between five political attitudes and two variants of political participation, our findings indicate that it is much more likely that political participation strengthens political attitudes than that attitudes trigger participation. This does not mean that attitudes are irrelevant for behaviour, but the reverse impact is much stronger. More specifically, we find that the effects of being politically engaged on political interest, efficacy, confidence and norms of citizenship are clearly stronger than the effects of these attitudes on participation.