The two-sample t test versus satterthwaite's approximate f test

A comparison between the two-sample t test and Satterthwaite's approximate F test is made, assuming the choice between these two tests is based on a preliminary test on the variances. Exact formulas for the sizes and powers of the tests are derived. Sizes and powers are then calculated and compared for several situations.     

The Volatility of Realized Volatility

In recent years, with the availability of high-frequency financial market data modeling realized volatility has become a new and innovative research direction. The construction of “observable” or realized volatility series from intra-day transaction data and the use of standard time-series techniques has lead to promising strategies for modeling and predicting (daily) volatility. In this article, we show that the residuals of commonly used time-series models for realized volatility and logarithmic realized variance exhibit non-Gaussianity and volatility clustering. We propose extensions to explicitly account for these properties and assess their relevance for modeling and forecasting realized volatility. In an empirical application for S&P 500 index futures we show that allowing for time-varying volatility of realized volatility and logarithmic realized variance substantially improves the fit as well as predictive performance. Furthermore, the distributional assumption for residuals plays a crucial role in density forecasting.     

Sequential Pattern Analysis: A Statistical Investigation of Sequence Length and Support

In sequential pattern analysis, the frequency of patterns is evaluated by the support. While computed efficiently from large databases, we show that the support cannot be compared between different databases, since it is influenced by the actual sequence length distribution. Models for this sequence length distribution are surveyed. One of these models, the Good distribution, appears to be sufficiently flexible for practice. It is used to exemplify an approach for adjusting the relative support such that the resulting adjusted support values are better comparable between different databases. We illustrate our findings with texts from the bilingual FinDe corpus.     

The Interplay Between Adolescents' Friendships and the Exchange of Help: A Longitudinal Multiplex Social Network Study

The aim of this study was to unravel the interrelatedness of friendship and help, and to examine the characteristics of friendship and help networks. The effects of mutual versus one‐sided help relations on friendship initiation and maintenance, and vice versa, were examined. Friendship and help networks were analyzed (N = 953 students; 41 classrooms; M_age = 12.7). The results illustrate that friendship and help networks show some similarities, but only partly overlap and have distinct characteristics. Longitudinal multiplex social network analyses showed that mutual help was important for the maintenance of friendship, but not for the initiation of friendship. Further, particularly mutual friendships provided a context in which help took place. Implications of these findings are discussed.     

Inaction over retractions of identified fraudulent publications: ongoing weakness in the system of scientific self-correction

Published articles may be retracted when their findings are no longer considered reliable due to honest error, publication misconduct, or research misconduct. This article focuses on the case of a single serial violator of research and publication ethics in anesthesiology and critical care, which is widely publicized. A chain of events led to detection of misconduct that had substantial impact on the evidence base for the safety of hydroxyethyl starch, an intravenous artificial colloid solution, which is reflected in current guidelines on fluid management and volume resuscitation. As citations to retracted works continue to be a cause for concern, this article reviews the retraction status of this author’s published articles to determine whether sufficient action has been taken to retract his body of work. Results show that retraction practices are not uniform and that guidelines for retraction are still not being fully implemented, resulting in retractions of insufficient quantity and quality. As retractions continue to emerge for the author’s publications, with ten more since 2011, and as they are generally increasing, these data on retractions not only provide findings of misconduct, but also allow us to make inferences about ongoing weaknesses in the system of scientific literature.     

The effects of leadership change on team escalation of commitment

Although teams benefit from developing plans and processes that boost efficiency and reduce uncertainty, they may become too attached to these plans and escalate commitment when an alternative response is needed. Drawing on theories of team leadership, team processes and escalation of commitment, we propose that a change in leadership can help the team reduce commitment to outdated plans and avoid further escalation over time. Across two studies, we tested and found support for our hypotheses and provide evidence that leadership change can break the cycle of escalation by enhancing leader-driven team reflection and refocusing the team on error correction instead of additional investment. We discuss how the results of these studies extend existing theory and add to our understanding of the important role leaders play in enhancing team adaptation and preventing team escalation.     

Spatial approaches to social work – theoretical foundations and implications for practice and research

ABSTRACT

Spatial approaches have inspired and grounded the social sciences and social geography already for a longer time. Beyond these models, the theory discourse on social work developed innovative concepts and models of socio-spatial approaches. They set a special focus on aspects of individual and social development, the concept of acquirement and emancipatory approaches to spatial design. For interventions, special methods for socio-spatial analyses were developed. This article reflects the main approaches of this theory discourse and asks for its key implications for social work practice and research.     

Capturing Relatedness: Comprehensive Measures based on Secondary Data

This paper presents new measures of technological and customer‐side relatedness constructed from widely available secondary data. Relatedness is a concept central to predicting the existence and nature of a relationship between corporate diversification and firm performance. Yet, finding appropriate measures has been an ongoing struggle. The widely used SIC‐based entropy measure has low construct validity, and survey‐based measures are hard to replicate across firms and industries and over time. The measures we develop significantly outperform established measures in explaining variation in firm performance across firms and over time, and both sources of relatedness are found to be independent and significant explanations of firm performance.