Analyzing survival data in conjunction with time-dependent surrogate endpoints in clinical trials

Current survival techniques do not provide a good method for handling clinical trials with a large percent of censored observations. This research proposes using time-dependent surrogates of survival as outcome variables, in conjunction with observed survival time, to improve the precision in comparing the relative effects of two treatments on the distribution of survival time. This is in contrast to the standard method used today which uses the marginal density of survival time, T. only, or the marginal density of a surrogate, X, only, therefore, ignoring some available information. The surrogate measure, X, may be a fixed value or a time-dependent variable, X(t). X is a summary measure of some of the covariates measured throughout the trial that provide additional information on a subject's survival time. It is possible to model these time-dependent covariate values and relate the parameters in the model to the parameters in the distribution of T given X. The result is that three new models are available for the analysis of clinical trials. All three models use the joint density of survival time and a surrogate measure. Given one of three different assumed mechanisms of the potential treatment effect, each of the three methods improves the precision of the treatment estimate.     

State Capacity,Conflict, and Development

The absence of state capacities to raise revenue and to support markets is a key factor in explaining the persistence of weak states. This paper reports on an ongoing project to investigate the incentive to invest in such capacities. The paper sets out a simple analytical structure in which state capacities are modeled as forward looking investments by government. The approach highlights some determinants of state building including the risk of external or internal conflict, the degree of political instability, and dependence on natural resources. Throughout, we link these state capacity investments to patterns of development and growth.     

The impact of migration on the nonmetropolitan population age structure, 1960–1990

In this paper we examine the short-run impact of migration on the age composition of nonmetropolitan areas. Changes in age structure can have important consequences at the local level, and the influence of migration is particularly notable because it is highly age-graded, with different migration patterns found in various types of nonmetropolitan communities. Here we compare the impact of migration on age structures in metropolitan and nonmetropolitan areas across the last three decades. Within nonmetropolitan areas we also compare counties with colleges, commuting counties, agricultural counties and retirement counties. We conclude that several factors influence the impact of migration on age structure. Impacts will be greater in smaller than in larger population groups, and in areas that specialize in economic functions that impinge on a particular age group. But in general, migration adds young people to metropolitan areas and older people to nonmetropolitan areas. Differential impacts may be lessened in periods, such as 1970–80, when substantial population redistribution was underway. Nevertheless, prior and present fertility and mortality trends, and the cumulative history of migration well exceed the impact of migration on age in any ten-year interval.Abbreviations Metro Metropolitan - Nonmetro Nonmetropolitan An earlier version of this paper was presented at the annual meeting of the Western Regional Science Association, Wailea, Hawaii, 22 February 1993.     

Are Parents Investing Less Time in Children? Trends in Selected Industrialized Countries

Trends in parental time invested in children since the 1960s are examined in 16 industrialized countries using time-use survey data. Despite the time pressures that confront today's families, parents appear to be devoting more time to children than they did 40 years ago. Results also suggest that mothers continue to devote more time to childcare than fathers, but the gender gap has been reduced. The consistency of these results across countries suggests a global trend toward an increase in parental time investment in children. Multivariate analysis of trends in parental time by type of activity was undertaken for Canada. It revealed a significant increase in parental time even after controlling for changes in the demographic composition of the population during the past few decades.     

Leadership, self, and identity: A review and research agenda

This article reviews empirical research on the role of follower self-conception in leadership effectiveness, and specifies an agenda for future research in this area. The review shows that several aspects of follower self-conception (i.e., self-construal, self-efficacy, self-esteem, and self-consistency) may be affected by leadership, and may mediate the effects of leadership on follower behavior. There also is consistent evidence that follower self-construal moderates the impact of leadership on follower attitudes and behavior. Two key themes for future research are defined. First, future research should focus on the development of theory about the role of relational self-construal in the leadership process. Second, it seems particularly valuable to develop theory about the interplay of different aspects of follower self-conception in leadership effectiveness, including the interactive effects of these aspects of self. Working backwards from these theoretical models of follower self-conception, specific leader behavior relevant to these aspects of self should then be identified.     

Governance for reconstruction in Africa: challenges for policy communities and coalitions

This article seeks to advance analyses and responses to conflict prevention and reconstruction in Africa that go beyond state‐centric perspectives to include a range of non‐state players. Drawing on examples from both Uganda and Canada, it focuses on the activities of NGOs that have ‘partnered’ with state‐based actors in various peacekeeping and peace‐building operations as well as on the increasingly important role played by think‐tanks. The latter have emerged in Africa as major contributors to the proliferating literature on the political economy of violence, an approach that recognizes that African conflict reflects imperatives of production and consumption in relations that juxtapose Africa’s political institutions and cultures with international and global political economies. The article argues that novel forms of ‘security communities’ are emerging from the non‐state/state/international partnerships and coalitions that have developed around contemporary issues like ‘blood’ diamonds, small arms, debt and HIV/AIDS, thus drawing attention to connections between conflict and development.     

What do we know about the timing of fertility transitions in europe?

The Princeton project on the decline of fertility in Europe (the European Fertility Project) suggested that this historical fertility transition occurred virtually simultaneously in a wide variety of economic and social environments. This finding has been cited widely as evidence for an innovation/diffusion view of fertility transitions. We demonstrate that the demographic methods used to date the fertility transition in Europe—primarily I_g, and (to a lesser extent) the Coale-Trussell M&m indices—may fail to detect the initial stages of a fertility transition and therefore cannot be used as the basis for strong statements about the timing of transitions. We review these measurement problems and their implications for the current understanding of the European fertility transition.     

A new dimension to nonparametric tests

It is demonstrated that a statistician can take a preliminary peek- at the data in a special vay in order to select an appropriate nonparametric test statistic without spoiling the distribution-free property. This process (adaptive selection and then testing) generally improves zhe paver over a vide range of underlying distributions and is the nev -dimension to nonparametric tests. Several illustrations are given using standard nonparametric techniques involving the usual one-sample, tvo-sample, k-sample, and independence testing situations. More recent (and not standard) applications to regression and classification problems are then considered. Finally one 'difficulty concerning this adapting process is noted, but a corrective action is suggested.     

Efficiency bounds for a generalization of ranked-set sampling

Abstract

Partially rank-ordered set sampling (PROSS) is a generalization of ranked-set sampling (RSS) in which the ranker is not required to give a full ranking in each set. In this paper, we compare the efficiency of the sample mean as an estimator of the population mean under PROSS, RSS, and simple random sampling (SRS). We find that for fixed set size and total sample size, the efficiency of PROSS falls between that of SRS and that of RSS. We also develop a method for finding a sharp upper bound on the efficiency of PROSS relative to SRS for a particular design.