Comparison of estimators in nested case–control studies with multiple outcomes

Reuse of controls in a nested case-control (NCC) study has not been considered feasible since the controls are matched to their respective cases. However, in the last decade or so, methods have been developed that break the matching and allow for analyses where the controls are no longer tied to their cases. These methods can be divided into two groups; weighted partial likelihood (WPL) methods and full maximum likelihood methods. The weights in the WPL can be estimated in different ways and four estimation procedures are discussed. In addition, we address modifications needed to accommodate left truncation. A full likelihood approach is also presented and we suggest an aggregation technique to decrease the computation time. Furthermore, we generalize calibration for case-cohort designs to NCC studies. We consider a competing risks situation and compare WPL, full likelihood and calibration through simulations and analyses on a real data example.     

Exact Inference in the Proportional Hazard Model: Possibilities and Limitations

It is suggested that inference under the proportional hazard model can be carried out by programs for exact inference under the logistic regression model. Advantages of such inference is that software is available and that multivariate models can be addressed. The method has been evaluated by means of coverage and power calculations in certain situations. In all situations coverage was above the nominal level, but on the other hand rather conservative. A different type of exact inference is developed under Type II censoring. Inference was then less conservative, however there are limitations with respect to censoring mechanism, multivariate generalizations and software is not available. This method also requires extensive computational power. Performance of large sample Wald, score and likelihood inference was also considered. Large sample methods works remarkably well with small data sets, but inference by score statistics seems to be the best choice. There seems to be some problems with likelihood ratio inference that may originate from how this method works with infinite estimates of the regression parameter. Inference by Wald statistics can be quite conservative with very small data sets.     

Populism and social media: how politicians spread a fragmented ideology

Populism is a relevant but contested concept in political communication research. It has been well-researched in political manifestos and the mass media. The present study focuses on another part of the hybrid media system and explores how politicians in four countries (AT, CH, IT, UK) use Facebook and Twitter for populist purposes. Five key elements of populism are derived from the literature: emphasizing the sovereignty of the people, advocating for the people, attacking the elite, ostracizing others, and invoking the ‘heartland’. A qualitative text analysis reveals that populism manifests itself in a fragmented form on social media. Populist statements can be found across countries, parties, and politicians’ status levels. While a broad range of politicians advocate for the people, attacks on the economic elite are preferred by left-wing populists. Attacks on the media elite and ostracism of others, however, are predominantly conducted by right-wing speakers. Overall, the paper provides an in-depth analysis of populism on social media. It shows that social media give the populist actors the freedom to articulate their ideology and spread their messages. The paper also contributes to a refined conceptualization and measurement of populism in future studies.     

Maximum flows in generalized processing networks

Processing networks (cf. Koene in Minimal cost flow in processing networks: a primal approach, 1982) and manufacturing networks (cf. Fang and Qi in Optim Methods Softw 18:143–165, 2003) are well-studied extensions of traditional network flow problems that allow to model the decomposition or distillation of products in a manufacturing process. In these models, so called flow ratios \(\alpha _e \in [0,1]\) are assigned to all outgoing edges of special processing nodes. For each such special node, these flow ratios, which are required to sum up to one, determine the fraction of the total outgoing flow that flows through the respective edges. In this paper, we generalize processing networks to the case that these flow ratios only impose an upper bound on the respective fractions and, in particular, may sum up to more than one at each node. We show that a flow decomposition similar to the one for traditional network flows is possible and can be computed in strongly polynomial time. Moreover, we show that there exists a fully polynomial-time approximation scheme (FPTAS) for the maximum flow problem in these generalized processing networks if the underlying graph is acyclic and we provide two exact algorithms with strongly polynomial running-time for the problem on series–parallel graphs. Finally, we study the case of integral flows and show that the problem becomes \({\mathcal {NP}}\)-hard to solve and approximate in this case.     

Strategic Experimentation with Exponential Bandits

We analyze a game of strategic experimentation with two‐armed bandits whose risky arm might yield payoffs after exponentially distributed random times. Free‐riding causes an inefficiently low level of experimentation in any equilibrium where the players use stationary Markovian strategies with beliefs as the state variable. We construct the unique symmetric Markovian equilibrium of the game, followed by various asymmetric ones. There is no equilibrium where all players use simple cut‐off strategies. Equilibria where players switch finitely often between experimenting and free‐riding all yield a similar pattern of information acquisition, greater efficiency being achieved when the players share the burden of experimentation more equitably. When players switch roles infinitely often, they can acquire an approximately efficient amount of information, but still at an inefficient rate. In terms of aggregate payoffs, all these asymmetric equilibria dominate the symmetric one wherever the latter prescribes simultaneous use of both arms.     

Transport Policy Scenarios for the EU: 2020 Images of the Future

It is essential to take a longer term view if sustainable mobility is to become a reality. This paper takes a perspective to 2020 and constructs Images of the future which conform to the principles of sustainable mobility. Set at the EU level, clear environmental, regional development and efficiency targets are set, within which strategies are developed, based on different combinations of technological innovation and the decoupling of economic growth from transport growth. The external political situation is taken as given with either a move towards greater co-operation (and extension) or towards greater fragmentation (and regionalisaization) in Europe. The three Images of the future (2020) demonstrate that challenging targets for sustainable mobility can be achieved through a range of different policy actions within the transport sector and more widely. Immediate action is required and even more difficult choices will have to be made in the EU 15, if large-scale extension of the EU takes place. Improvements in vehicle technology alone will not achieve the targets. More fundamental changes have to take place in the way in which people make travel choices and in the means by which freight is transported. All of these measures must involve less travel, more efficient and cleaner travel modes.     

Do the Married Really Live Longer? The Role of Cohabitation and Socioeconomic Status

Numerous studies have shown that married women and men experience the lowest mortality. Legal marital status, however, does not necessarily reflect today's social reality because individuals are classified as never married, widowed, or divorced even when they are living with a partner. Denmark is one of the forerunners of developments in coresidential partnerships and one of only a few countries where administrative sources provide individual‐level information on cohabitation for the whole population. Using register information from Statistics Denmark on 3,888,072 men and women ages 18–65, the author investigated mortality differences by living arrangement with hazard regression models. Overall, premature mortality was found to be lowest for married persons, followed by cohabiting persons. Adjusting for socioeconomic status reduced excess mortality of nonmarried individuals. Moreover, a mortality‐crossover effect emerged in which cohabiters with above‐average socioeconomic status had a lower risk of dying than married people. This finding was particularly pronounced for men.     

A procedural model of voting

The formal framework of social choice theory is generalized through the introduction of separate representations of preferences and choices. This makes it possible to treat voting as a procedure in which decisions are actually made by interacting participants, rather than as a mere mechanism for aggregation. The extended framework also allows for non-consequentialist preferences that take procedural factors into account. Concepts such as decisiveness, anonymity, neutrality, and stability are redefined for use in the new context. The formal results obtained confirm the universality of strategic voting.