Estimating percentile-specific treatment effects in counterfactual models: a case-study of micronutrient supplementation, birth weight and infant mortality

Summary.  Clinical trials of micronutrient supplementation are aimed at reducing the risk of infant mortality by increasing birth weight. Because infant mortality is greatest among the low birth weight (LBW) infants (2500 g or under), an effective intervention increases the birth weight among the smallest babies. The paper defines population and counterfactual parameters for estimating the treatment effects on birth weight and on survival as functions of the percentiles of the birth weight distribution. We use a Bayesian approach with data augmentation to approximate the posterior distributions of the parameters, taking into account uncertainty that is associated with the imputation of the counterfactuals. This approach is particularly suitable for exploring the sensitivity of the results to unverifiable modelling assumptions and other prior beliefs. We estimate that the average causal effect of the treatment on birth weight is 72 g (95% posterior regions 33–110 g) and that this causal effect is largest among the LBW infants. Posterior inferences about average causal effects of the treatment on birth weight are robust to modelling assumptions. However, inferences about causal effects for babies at the tails of the birth weight distribution can be highly sensitive to the unverifiable assumption about the correl-ation between the observed and the counterfactuals birth weights. Among the LBW infants who have a large causal effect of the treatment on birth weight, we estimate that a baby receiving the treatment has 5% less chance of death than if the same baby had received the control. Among the LBW infants, we found weak evidence supporting an additional beneficial effect of the treatment on mortality independent of birth weight.     

The positional power of nodes in digraphs

Many economic and social situations can be represented by a digraph. Both local and global methods to determine the strength or power of all the nodes in a digraph have been proposed in the literature. We propose a new method, where the power of a node is determined by both the number of its successors and the powers of its successors. Our method, called the positional power function, determines a full ranking of the nodes for any digraph. The positional power function can either be determined as the unique solution to a nonhomogeneous system of equations, or as the limit point of an iterative process. The solution can easily be obtained explicitly, which enables us to derive a number of interesting properties of the positional power function. We also consider the Copeland variant of the positional power function. Finally, we extend our method to the class of all weighted graphs.The authors like to thank two anonymous referees for their valuable comments. The first author would like to thank the Netherlands Organisation for Scientific Research (NWO) for financial support.     

The extent and limits of solidarity in Dutch health care

Solidarity and equal access are twin principles in the Dutch health care system: solidarity between the rich and poor and among people with high and low risks formally guarantees equal access to health care services. However, in the past few years government policies, guided by the ideology of market reform and free choice, have resulted in patterns of inequality that favour privately insured over sickness fund insured. In the meantime, the level of public support for the principles of solidarity and equal access is dropping. A significantly larger portion of the Dutch people now believes that it would be too costly to grant everyone the right to all medical treatments possible. An important reason for the decline of solidarity and equal accessibility is the scarcity of resources. The scarcity of resources and the waiting lists resulting from it will reduce the extent of the benefits package and the access to the care services of the health system. The better-off will have the resources to receive care services that are not part of the basic package. Moreover, the scarcity of resources will affect the readiness in society to provide informal care. Opposed to the compulsory macro solidarity of the health insurance system, informal care is based on a voluntary kind of solidarity in which personal choice plays an important role. Waiting lists and diminishing professional support weaken this readiness, as such support is a necessary condition for informal carers to keep caring for their relatives and friends. Because the informal care system is a necessary supplement to the formal system of care, the lack of help offered by the latter will in the end endanger the solidarity not only in informal care, but in the institutional care system as well.     

Formulating waste management strategies based on waste management practices of households in Santiago de Cuba, Cuba

Rapid urbanisation, population growth and changes in lifestyles in low- and middle-income countries contribute to increasing the per capita domestic waste generation. This trend leads to deplorable environmental and public health conditions, especially in rapidly expanding cities of low- and middle-income countries lacking appropriate waste management systems, Santiago de Cuba is no exception. To improve solid waste management in the city of Santiago de Cuba, the generation of household waste was studied and individual waste treatment approaches were assessed. The principle of a household level analysis was adopted to enable the development of strategies based on the specific conditions of households, their awareness and needs.In February 2004, a survey covering 1180 households was conducted on issues such as monthly consumed goods, waste generated and its treatment. The waste generated by the households was subsequently assessed by means of a measuring campaign. The measured volume not only comprised the collected waste fraction but also the waste materials treated on-site or recovered and recycled by all the different means available.The paper contains the results of the composition and distribution of the waste generated by the households as a function of socio-demographic data. Furthermore, the paper describes the various household treatment strategies dependent on specific waste material types. Several types of household waste can be differentiated by statistical cluster analysis. These household types are characterised not only by the amount of waste generated but also by socio-economic status and waste treatment practices. The results obtained are used to develop a range of waste management strategies, each relating to a household type and characterised by its generated amount, waste material type and spatial urban distribution. Since the strategies are adapted to the requirements and needs of the households, they are more readily accepted by the population concerned. Such socially anchored strategies will contribute to improving the waste situation in the city of Santiago de Cuba and allow an optimised allocation of local resources.     

生物多样性保护的新概念：参与性自然资源监测

参与性自然资源监测是一种新理念下以村民为主体的对社区所依赖资源进行监测的系统。它以掌握自然资源的丰富程度和利用及其变化情况，增强村民环境意识并改善村民和自然保护区之间关系为目的，具有简便易行、应用乡土知识、资源投入低、决策透明的优点，能够促进森林资源保护、监测和管理，进行意识教育、冲突管理、野生动物肇事管理和促进当地经济发展。     

Survey non-response and the duration of unemployment

Summary.  Social surveys are often used to estimate unemployment duration distributions. Survey non-response may then cause a bias. We study this by using a data set that combines survey information of individual workers with administrative records of the same workers. The latter provide information on durations of unemployment and personal characteristics of all survey respondents and non-respondents. We develop a method to distinguish empirically between two explanations for a bias in results based on only survey data: selectivity due to related unobserved determinants of durations of unemployment and non-response and a causal effect of a job exit on non-response. The latter may occur even in fully homogeneous populations. The methodology exploits variation in the timing of the duration outcome relative to the survey moment. The results show evidence for both explanations. We discuss implications for standard methods to deal with non-response bias.