Bayesian measures of model complexity and fit

Summary. We consider the problem of comparing complex hierarchical models in which the number of parameters is not clearly defined. Using an information theoretic argument we derive a measure p _D for the effective number of parameters in a model as the difference between the posterior mean of the deviance and the deviance at the posterior means of the parameters of interest. In general p _D approximately corresponds to the trace of the product of Fisher's information and the posterior covariance, which in normal models is the trace of the 'hat' matrix projecting observations onto fitted values. Its properties in exponential families are explored. The posterior mean deviance is suggested as a Bayesian measure of fit or adequacy, and the contributions of individual observations to the fit and complexity can give rise to a diagnostic plot of deviance residuals against leverages. Adding p _D to the posterior mean deviance gives a deviance information criterion for comparing models, which is related to other information criteria and has an approximate decision theoretic justification. The procedure is illustrated in some examples, and comparisons are drawn with alternative Bayesian and classical proposals. Throughout it is emphasized that the quantities required are trivial to compute in a Markov chain Monte Carlo analysis.     

Equal representation in two-tier voting systems

The paper investigates how voting weights should be assigned to differently sized constituencies of an assembly. The one-person, one-vote principle is interpreted as calling for a priori equal indirect influence on decisions. The latter are elements of a one-dimensional convex policy space and may result from strategic behavior consistent with the median voter theorem. Numerous artificial constituency configurations, the EU and the US are investigated by Monte–Carlo simulations. Penrose’s square root rule, which originally applies to preference-free dichotomous decision environments and holds only under very specific conditions, comes close to ensuring equal representation. It is thus more robust than previously suggested.     

英汉文化趋同与语言文化差异

文章从文化与语言两方面论述了中西文化的趋同现象,在文化趋同的过程中语言文化差异必然存在.不同的文化在趋同中发展,在差异中共存.     

大学生心理健康与体育锻炼

文章通过对大学生心理现状和影响因素的分析,结合对体育锻炼功能的探讨,得出体育锻炼对大学生心理健康有积极作用的结论.     

A Bayesian approach to Markov modelling in cost-effectiveness analyses: application to taxane use in advanced breast cancer

Summary. The paper demonstrates how cost-effectiveness decision analysis may be implemented from a Bayesian perspective, using Markov chain Monte Carlo simulation methods for both the synthesis of relevant evidence input into the model and the evaluation of the model itself. The desirable aspects of a Bayesian approach for this type of analysis include the incorporation of full parameter uncertainty, the ability to perform all the analysis, including each meta-analysis, in a single coherent model and the incorporation of expert opinion either directly or regarding the relative credibility of different data sources. The method is described, and its ease of implementation demonstrated, through a practical example to evaluate the cost-effectiveness of using taxanes for the second-line treatment of advanced breast cancer compared with conventional treatment. For completeness, the results from the Markov chain Monte Carlo simulation model are compared and contrasted with those from a classical Monte Carlo simulation model.     

The Gatekeeping Function of Trust in Cross‐sector Social Partnerships

Hunger and deprivation, lack of education, sanitation, and health care are only a few pressing issues related to poverty in developing countries. Addressing such complex social issues requires pooling complementary resources of the civil, public, and private sector. Over the last decade, stakeholders tried to cocreate innovative solutions in cross‐sector social partnerships (CSSPs) at the base of the economic pyramid (BoP), but collaboration proved to be very challenging. Practitioners become increasingly frustrated with operational differences, intransparency, and mismatched goals in partnerships. This study unravels the black box of collaboration and delivers empirical insights on trust and power in CSSPs based on social exchange theory. Structural equation modeling (SEM) enables us explore relationships beyond case‐based insights. Our rigorous empirical analysis covers 207 interorganizational relationships and outlines a crucial gatekeeping function of trust in CSSPs. Findings provide strong empirical support for conceptual works calling for an “integrative orientation” in CSSPs. Furthermore, we pinpoint the role of intermediates and draw implications for future research.     

Determinants of short-term value creation for the bidder: evidence from France

This paper analyses bidder short-term returns of 58 takeover bids that occur between 1997 and 2005 on the French market. Furthermore, the determinants of this performance are examined to improve understanding of the sources of value creation or destruction arising from M&A. This study reports that M&A are typically friendly, horizontal transaction, and relate to the entire target capital. The event study methodology is used to estimate bidder value creation. Three findings are shown in this study. First, we find strong evidence that the announcement of a takeover bid generates significant, high returns for the bidder with prebid blockholder position in the target (toehold) versus the bidder without toehold. In this case, there is a strong presumption that the synergies’ motive is the prime reason for the offer. Second, these results show that bidders with low potential growth positively influence share price around the bid announcement. In addition, the growth profile of the target is associated with value creation for the bidder.     

Shareholder activism among portfolio managers: rational decisions or 15 minutes of fame?

This paper investigates shareholder activism by observing Swedish portfolio managers’ behavior at firms’ annual general meetings. Institutional shareholders’ voting behavior and tendencies for raising opinions at the general meetings are related to firm characteristics, suggested by both agency theory and institutional perspectives. The results show that institutional shareholders are more likely to be active in large firms, which appear a lot in media, and have a large proportion of institutional ownership. Portfolio managers appear not to consider bad firm performance as a reason for targeting firms. Instead, managers’ behavior is consistent with the institutional notion that they benefit from the activism themselves, without trying to improve target firms’ performance. In view of this notion, it is rational for managers to be active in large firms, with large media coverage, achieving their 15 minutes of fame at the general meetings.     

An improved time-space lower bound for tautologies

We show that for all reals c and d such that c ² d<4 there exists a positive real e such that tautologies of length n cannot be decided by both a nondeterministic algorithm that runs in time n ^c , and a nondeterministic algorithm that runs in time n ^d and space n ^e . In particular, for every \(d<\sqrt[3]{4}\) there exists a positive e such that tautologies cannot be decided by a nondeterministic algorithm that runs in time n ^d and space n ^e .