Performance of goodness-of-fit tests for the Cox proportional hazards model with time-varying covariates

There are few readily-implemented tests for goodness-of-fit for the Cox proportional hazards model with time-varying covariates. Through simulations, we assess the power of tests by Cox (J R Stat Soc B (Methodol) 34(2):187–220, 1972), Grambsch and Therneau (Biometrika 81(3):515–526, 1994), and Lin et al. (Biometrics 62:803–812, 2006). Results show that power is highly variable depending on the time to violation of proportional hazards, the magnitude of the change in hazard ratio, and the direction of the change. Because these characteristics are unknown outside of simulation studies, none of the tests examined is expected to have high power in real applications. While all of these tests are theoretically interesting, they appear to be of limited practical value.     

Voluntary Associations Within the Local Political Context: How Characteristics of the Organizations and the Local Governments Influence Perceptions of Success

A cornerstone of democracy is the capacity of citizens to influence political decisions either through elections or by making their will known in the periods between elections. The aim of the present study is twofold: (1) to explore what factors inherent of the voluntary associations that determine the perceived success in their attempts to influence policy and (2) to investigate what role the composition of the local government have on the perceived success. This study is based on a survey conducted among 404 local voluntary associations in four different municipalities in Sweden. The results show that the frequency contacts influence perceived success positively, while the level of civic engagement of the voluntary associations affected the perceived success negatively. Having a heterogeneous local government also contributed positively to the perceived success to influence policy.     

日本移动影音的商业模式探析

在移动影音产业既有的成功商业模式之中,日本经验常被提及,其主要经营模式被归类为"免费播放"。一般认为,正是通过"免费播放"这种方式,才能从一开始就顺利实现让消费者对于移动电视由认识、接受到使用的历程。然而,日本移动电视之所以成功,并非完全归功于免费播放,还另有原因。     

Estimating two-stage network Slacks-based inefficiency: An application to Bangladesh banking

This paper studies the performance of nineteen private commercial banks and two government-owned banks in Bangladesh during the period 2005–2008 using a slacks-based inefficiency measure and the directional technology distance function. Performance is measured assuming a black-box production structure and then the black-box is opened and examined using a two stage network production structure. Current period performance in maximizing desirable loans and securities investments and minimizing bad loans depends on how efficiently inputs at one stage of production are transformed into intermediate outputs which are used at a subsequent stage of production. In addition, current period production of the intermediate output is constrained by the amount of non-performing loans that were generated in an earlier period.     

Book reviews

Distributed Cognitions: Psychological and Educational Considerations. Gavriel Salomon (Ed.), Cambridge & New York: Cambridge University Press, 1993. 275 pages, $49.95.

The Computer as Medium. Peter Bøgh Andersen, Berit Holmqvist, & Jens F. Jensen (Eds.), Cambridge: Cambridge University Press. 495 pages. $54.95.