天山北坡经济带人与自然生态协调发展的实证分析

作为可持续发展的重要组成部分,人与自然生态的协调发展意义重大。作为新疆经济最发达的地区之一,天山北坡经济带中人与自然生态的发展状况处于何种阶段,不协调的因素有哪些,是否能适应可持续发展的要求,近来成为经济学家探讨的热门话题。本文从人口、资源、环境三个系统间的协调程度入手,借助历史数据,运用协调系数法和主成分分析法对天山北坡经济带人与自然生态的协调发展进行实证分析。     

The duration of unemployment in Russia

This paper uses longitudinal survey data to assess factors affecting the duration of unemployment in Russia. We examine four types of marginalised labour force participants, according to ILO guidelines and survey responses, and we estimate duration models for each type. It turns out that the sets of characteristics with the strongest effects on the duration are remarkably similar across the different unemployment definitions and model specifications. Therefore, despite the formidable practical measurement problems, problematic groups of individuals can actually be identified. Received: 27 January 1999/Accepted: 27 January 2000     

Fertility assimilation of immigrants: Evidence from count data models

This study applies count data estimation techniques to investigate the fertility adjustment of immigrants in the destination country. Data on completed fertility are taken from the 1996 wave of the German Socioeconomic Panel (GSOEP). While the economic literature stresses the role of prices and incomes as determinants of fertility, the demographic literature discusses whether assimilation or disruption effects dominate immigrants' fertility after migration. We find evidence in favor of the assimilation model according to which immigrant fertility converges to native levels over time. In addition, we confirm the negative impact of female human capital on fertility outcomes. Received: 7 January 1999/Accepted: 10 August 1999     

Modelling household income dynamics

This paper is about income and poverty dynamics and their socioeconomic correlates. The first half of the paper aims to establish some of the salient facts for Britain, applying the pioneering methods of Bane and Ellwood (1986). Important for poverty dynamics are changes in labour earnings from persons other than the household head, changes in non-labour income (including benefits), and changes in household composition, in addition to changes in the heads' labour earnings. The second half of the paper is a review and critique of the multivariate modelling frameworks which might be used to explain and forecast these salient facts for Britain or elsewhere. Received: 7 January 1999/Accepted: 22 July 1999     

Education funding and regional convergence

The aim of this paper is to discuss the process of regional convergence within the framework of an overlapping generations model in which the engine of growth is the accumulation of human capital. In particular, we consider different education funding systems and compare their performance in terms of growth rates and pace of convergence between two heterogeneous regions. The analysis suggests that the choice of a particular education system incorporates a possible trade-off between long run growth rate and short run convergence. In such choice, the initial capital stock and the extent of regional human capital discrepancy appear as central variables. Received: 27 January 1999/Accepted: 16 April 1999     

基于人口生态视野的贵州民族地区出生性别比失调问题研究

出生性别比是人口发展的"生态基础",而出生性别比失调问题是和谐人口生态关系的一个极不和谐的因素。已有的人口学研究一般从全国或区域的范围分析出生性别比问题,忽视了少数民族地区出生性别比失调自身的特点。基于人口生态视野分析贵州民族地区出生性别比失调的特征、成因和后果。男性偏好在该地区特定的人口生态制约下有着深刻的经济、文化、社会、性别根源。贵州民族地区综合治理出生性别比失调必须采取一系列措施,其中,提高贵州民族地区妇女社会地位具有根本性的意义。     

Ecosystem resilience, specialized adaptation and population decline: A modern Malthusian theory

The purpose of this article is to construct a theoretical framework characterizing the interactions among economic development, ecosystem equilibrium and possible population decline, and to discuss the population dynamics in the very long run. In our framework, economic activities bridge population and environment. On the one hand, human beings reform the environment through economic activities; on the other hand, economic activities decrease environmental resilience and increase the possibility of an environmental change in a discontinuous and irreversible pattern, as described in Arrow et al. (1995). Furthermore, a highly developed economy also causes over-specialization of human adaptation, which tends to exaggerate the impact of an environmental change on human population size. Received: 19 January 1999/Accepted: 3 July 1999     

Demographic change, endogenous labor supply and the political feasibility of pension reform

Options for reforming unfunded public pension schemes that are now being discussed all share the feature that the burden induced by demographic change would be shifted towards presently living and away from unborn generations. Existing models of the political economy of pension reform can not explain why such reform options are being discussed at all. We present an alternative model in which the possibility of evasion of workers from payment of social security taxes is taken into account by modelling a labor supply function. It turns out that the burden of demographic change may fall completely or at least predominantly on the pensioners. Thus this type of model can much better explain recent trends in legislature on unfunded public pension systems in industrial democracies. Received: 7 January 1999/Accepted: 20 December 1999     

Migration and foreign trade: Further results

In this note, we use the production-theory approach to immigration in an open-economy setting to investigate the role of nonresident workers in Swiss aggregate production. Unlike earlier work in this area, exports are explicitly taken into account. Indeed, a statistical test for global separability between inputs and outputs reveals that exports and products intended for domestic use cannot be aggregated. Our results show that immigration tends to stimulate imports and to shift the output mix towards nontraded goods, thereby impacting negatively on the trade account. Received: 24 March 1999/Accepted: 4 January 2001     

Saving behaviour and earnings uncertainty: Evidence from the British Household Panel Survey

For the first time, this paper uses a panel data set, the British Household Panel Survey, to analyse saving behaviour in Britain. One objective is to test the precautionary saving hypothesis, according to which households save to self-insure against uncertainty. Our results show that in accordance with this hypothesis, various measures of uncertainty based on earnings variability have a statistically significant effect on households' saving decisions. Moreover, in accordance with the life cycle model, households save more if they expect their financial situation to deteriorate. Received: 15 June 1999/Accepted: 4 January 2001     

Personal income taxation under mobility, exogenous and endogenous welfare weights, and asymmetric information

This paper analyses how governments should tax labour income accruing to a group of highly skilled and geographically mobile individuals who divide their time or career between several jurisdictions. The analysis differs from previous models on migration and taxation by addressing optimal regulation when agents work for several principals. Optimal taxation is developed for social welfare functions with exogenous and endogenous welfare weights. Marginal income taxes are applied for screening purposes, and the rates are lower with endogenous than with exogenous welfare weights. Received: 22 January 1998/Accepted: 3 July 1999)     

Incorporating physiology into parasitoid behavioral ecology: the allocation of nutritional resources

A critical problem faced by most theoretical studies of parasitoid behavior and population dynamics has been the paucity of empirically obtained information about the pattern of resource allocation to egg production and metabolic maintenance in relation to adult diet in female parasitoids. This review calls for a shift from traditional manipulative feeding studies to studies that quantify the energetic budget of parasitoids and which take into account the dynamic nature of metabolic processes. As guidelines, we highlight the advances made along these lines with other insect groups and some of the simplest tools already available today for fulfilling this goal. Received: December 22, 1998 / Accepted: January 12, 1999     

The relative risk aversion hypothesis of educational choice

Analysing young people's educational choices, we derive and test implications of a relative risk aversion hypothesis: that educational choices are made so as to minimize the risk of ending up with a lower level of education than one's parents. These implications are in general different from what one would expect from human capital theory. We use a unique data set which combines data from administrative registers on young people's pathways through the educational system and their family background with survey data on their academic abilities at lower secondary school. The evidence is partly in favour of the relative risk aversion hypothesis. Received: 19 August 1999/Accepted: 10 January 2001 All correspondence to Eskil Heinesen. We are grateful to Karin Blix Mogensen and Martin B?g for excellent research assistance, and to two anonymous referees, John F. Ermisch, Martin Browning, Michael Rosholm, Paul Bingley, and participants at the conference of the European Society for Population Economics in Turin, 1999, for valuable comments and suggestions. Responsible editor: John F. Ermisch.     

Modeling female fertility using inflated count data models

For modeling complete female fertility we propose a zero-and-two-inflated count data model, which accounts for a relative excess of both zero and two children. As the underlying distribution of counts we use the standard Poisson distribution and the more general Gamma count distribution. We compare our proposed model with standard count data models by using data on complete fertilities for a sample of Swedish women. The preferred specification for Swedish fertility data is the zero-and-two inflated Gamma count data model. The estimated “extra” probabilities of zero and two children, when modelled as individual specific probabilities, vary substantially across individuals, with mean of 0.05 and 0.16, respectively. These extra probabilities show that women who formed a family later in life have a higher probability of being childless, and women of our youngest cohort have a higher probability of forming a two-child family. Received: 7 January 1999/Accepted: 19 May 1999     

Parasitoid-mediated effects: apparent competition and the persistence of host–parasitoid assemblages

Indirect effects such as apparent competition (in which two hosts that do not compete for resources interact via a shared natural enemy) are increasingly being shown to be prevalent in the structure and function of ecological assemblages. Here, we review the empirical and theoretical evidence for these enemy-mediated effects in host–parasitoid assemblages. We first address questions about the design of experiments to test for apparent competition. Second, we consider factors likely to affect the coexistence of host species that share a parasitoid and are involved in apparent competition. We show that parasitoid aggregation, and the switching effect that this can generate when hosts occur in separate patches, not only promotes persistence but is also strongly stabilizing. The broader consequences of these effects are discussed. Received: November 6, 1998 / Accepted: January 13, 1999     

农村人口流动对农田生态建设的影响

本文从我国实际出发,分析了农村剩余劳动力流出及其回流对农田生态建设的影响,趋利避害,因势利导,为新形势下我国农田生态建设提出相应的建议,以期为我国经济建设提供良好的生态环境支持和强大的经济动力。     

Segregation and Fragmentation: Extending Landscape Ecology and Pattern Metrics Analysis to Spatial Demography

Though demography’s roots involve a strong spatial component, recent attention to capitalizing on widely available spatially referenced demographic data has returned the focus to spatially enabled analyses. Landscape ecology offers a theoretical framework and concomitant methodology in pattern metric analysis well suited for extracting process through the examination of spatial patterns. Applied on the environmental side of population–environment interaction research, pattern metric analysis has not been brought to bear on population data per se. This research illustrates the utility of a pattern metric approach utilizing U.S. Census data from 1990 and 2000 to document changes in spatial configuration of race and class in South Carolina. The results corroborate similar findings elsewhere of exurban growth as well as an increasing income gap and spread of Hispanic population, both statistically and spatially. Further insight into the forces related to these processes is gained from explicit assessment of spatial configuration. The method is offered as a complementary tool to the richly evolving field of spatial demography.     

Estimation of the probability of insect pest introduction through imported commodities

A quantitative risk assessment is needed for each quarantine pest insect to ensure quarantine security without sacrificing the transparency of international trade. The probability of introduction, which is defined as the probability that one or more reproductive individuals of a pest insect species pass the port, is one of the basic components determining the risk of pest invasion. The probability depends on two biological characteristics of pests: mode of reproduction and spatial distribution of insects per host plant. In this article, the probability of introduction was calculated for each of the following four categories: (1) bisexual, gregarious pests; (2) bisexual, solitary pests; (3) parthenogenetic, gregarious pests; and (4) parthenogenetic, solitary pests. Then, equations were derived to predict the effects of two prevention practices conducted before export: disinfestation treatment and the subsequent export sampling inspection of consignments. These equations also enable estimation of the probability of introduction under natural mortality, which thus can be used in place of the criterion of Maximum Pest Limit (MPL). The method was applied to the Mexican fruit fly Anastrepha ludens (Loew), as an example. The contour graph of the probability of introduction indicated the optimal combination of the intensity of two prevention practices that ensures a given security level. Existence of an antagonistic interaction was also indicated between the disinfestation treatment and the subsequent sampling inspection. Received: January 22, 1999 / Accepted: September 6, 1999     

Perspective of practical biological control and population theories

We have not yet had sufficient theoretical explanation for successful biological control in which a key pest is controlled after an introduction of natural enemies. I compare here real features of successful biological control and theoretical host–parasitoid population models to reduce the gap between theory and practice. I first review the historical interaction between classical biological control projects and theoretical population models. Second, I consider the importance of host refuges in host–parasitoid population dynamics as concerns the mechanisms of low and stable host density. The importance of density–dependent parasitism through parasitoid reproduction in multivoltine host–parasitoid systems and supplemental generalist natural enemies are also discussed. Finally, I consider the difference in tactics for classical biological control and for augmentation of natural enemies in annual crop systems. Received: December 20, 1998 / Accepted: January 15, 1999     

The socioeconomic consequences of young women's childbearing: Reconciling disparate evidence

Recent studies have begun to examine rigorously the links between early childbearing and subsequent socioeconomic status. Prominent in this literature has been a set of analyses that have used sibling fixed effects models to control for omitted variables bias. These studies report that the siblings difference procedure leads to smaller estimates of the effects of teen fertility than does standard regression analysis. While it is well known that the siblings fixed effects procedure makes strong assumptions regarding the type of omitted variables and is not necessarily robust to alternative assumptions, the assumptions of the procedure have not been explicitly examined. This paper uses 1979–1992 data from the National Longitudinal Survey of Youth to compare estimates of the income and education consequences of teenage and young adult fertility from standard regression and siblings fixed effects models with estimates from more general, alternative siblings models. Received: 19 January 1998/Accepted: 6 April 1999