We establish limit theory for the Grenander estimator of a monotone density near zero. In particular we consider the situation when the true density f(0) is unbounded at zero, with different rates of growth to infinity. In the course of our study we develop new switching relations using tools from convex analysis. The theory is applied to a problem involving mixtures. 相似文献
Urban Ecosystems - Urban green space can help mitigate the negative impacts of urban living and provide positive effects on citizens’ mood, health and well-being. Questions remain, however,... 相似文献
Urban expansion is creating environmental stressors through land use change, habitat fragmentation, and habitat loss. These stressors, along with a host of others, are driving precipitous declines in vertebrate taxa around the world. Amphibians, often requiring a narrow range of environmental conditions, can be especially susceptible to the stressors of environmental change. Despite habitat loss and degradation, some amphibian species continue to persist in altered urban landscapes. The red-backed salamander (Plethodon cinereus) is one such- species and in this study, we assess how habitat patch size affects population density and genetic diversity of salamander populations in and around an urban center in Ohio, United States. Further, we examined patterns of genetic differentiation and landscape connectivity to understand gene flow between populations and tested for historic demographic bottleneck effects. Populations were sampled from 9 urban forest patches ranging in size from less than 1 ha to approximately 250 ha. There was no apparent effect of contiguous habitat patch size on salamander density nor genetic diversity, but we did observe significant genetic differentiation between 97% of pairwise population comparisons. The differentiation observed was not a result of overland distance or effective distance due to landscape resistance. There was evidence of historic bottlenecks at every site. These results suggest that density is driven by within-patch heterogeneity and that genetic diversity is affected by drivers other than patch size or contemporary population density. Our study demonstrates that red-backed salamanders can persist in wooded, urban parks, but that genetic diversity remains susceptible to demographic changes.
Semiparametric maximum likelihood estimators have recently been proposed for a class of two‐phase, outcome‐dependent sampling models. All of them were “restricted” maximum likelihood estimators, in the sense that the maximization is carried out only over distributions concentrated on the observed values of the covariate vectors. In this paper, the authors give conditions for consistency of these restricted maximum likelihood estimators. They also consider the corresponding unrestricted maximization problems, in which the “absolute” maximum likelihood estimators may then have support on additional points in the covariate space. Their main consistency result also covers these unrestricted maximum likelihood estimators, when they exist for all sample sizes. 相似文献
Asuccessful revenue management system requires accurate demand forecasts for each customer segment. The forecasts are used to set booking limits for lower value customers to ensure an adequate supply for higher value customers. The very use of booking limits, however, constrains the historical demand data needed for an accurate forecast. Ignoring this interaction leads to substantial penalties in a firm's potential revenues. We review existing unconstraining methods and propose a new method that includes some attractive properties not found in the existing methods. We evaluate several of the common unconstraining methods against our proposed method by testing them on intentionally constrained simulated data. Results indicate our proposed method outperforms other methods in two of three data sets. We also test the revenue impact of our proposed method, expectation maximization (EM), and “no unconstraining” on actual booking data from a hotel/casino. We show that performance varies with the initial starting protection limits and a lack of unconstraining leads to significant revenue losses. 相似文献
We review limit theory and inequalities for the Kaplan–Meier Kaplan and Meier (J Am Stat Assoc 53:457–481, 1958) product limit
estimator of a survival function on the whole line . Along the way we provide bounds for the constant in an interesting inequality due to Biotouzé et al. (Ann Inst H Poincaré
Probab Stat 35:735–763, 1999), and provide some numerical evidence in support of one of their conjectures.
Supported in part by NSF grant DMS-0503822 and by NI-AID grant 2R01 AI291968-04. 相似文献
A modelling procedure is proposed for complex, dynamic household data structures where households change composition over time. Multilevel multiple membership models are presented for such data and their application is discussed with an example. 相似文献
ABSTRACT“Backyard” green infrastructure programs are an innovative way to manage urban stormwater, with many social and ecologic benefits. In many programs, however, residents with lower incomes are not reached, though they could benefit from participation, and though their participation could benefit the socioecological system. We examined awareness of and interest in backyard green infrastructure among lower- and moderate-income residents (N = 234). Awareness among our study population is low to moderate, but interest is moderate to high, with variability by some demographic and other characteristics. A spouse/partner, city agency, and/or neighbor may have influential roles in increasing participation in backyard green infrastructure. 相似文献