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61.
Jehad Al-jararha 《统计学通讯:模拟与计算》2013,42(8):1906-1916
A class of sampling two units without replacement with inclusion probability proportional to size is proposed in this article. Many different well known probability proportional to size sampling designs are special cases from this class. The first and second inclusion probabilities of this class satisfy important properties and provide a non-negative variance estimator of the Horvitz and Thompson estimator for the population total. Suitable choice for the first and second inclusion probabilities from this class can be used to reduce the variance estimator of the Horvitz and Thompson estimator. Comparisons between different proportional to size sampling designs through real data and artificial examples are given. Examples show that the minimum variance of the Horvitz and Thompson estimator obtained from the proposed design is not attainable for the most cases at any of the well known designs. 相似文献
62.
随着油气勘探程度的不断提高,未发现的剩余油气资源越来越少。如何准确预测高勘探程度即成熟探区的剩余油气资源,成为石油投资者和油气资源评价工作者关注的焦点。详细探讨了油藏规模序列法预测油气资源的原理、方法、操作流程及存在的问题,并运用该方法对东营凹陷剩余可探明储量以油气成藏体系为评价单元进行了预测。研究表明,东营凹陷剩余可探明储量约为17.03×108t,仍具有较高的勘探潜力,并且主要集中在东营中央背斜带和东营凹陷北坡两个油气成藏体系内。实践证明,由于油藏规模序列法合理回避了油气成因机理问题,减少了资源评价工作中人为因素的影响,使资源评价结果更为客观。 相似文献
63.
AbstractA grain surplus and the grain trade are closely related to the urbanization of developing countries. However, existing literature has not given adequate attention to this issue. Our paper develops a theoretical model to explain the mechanisms whereby changes in the grain surplus constrain the level of urbanization in a closed economy context and the grain trade affects the level of urbanization by acting on the grain surplus in an open economy context. A test of the theoretical model applied to some developing countries in Asia during the period 1993-2010 shows that international trade is generally negatively correlated with level of urbanization. However, cereal and non-cereal trade vary in terms of their relation to urbanization: whereas the former is positively correlated with level of urbanization, the latter is negatively correlated with it. Since the net import of cereals relaxes the constraint imposed on the level of urbanization by the domestic grain surplus, it can have a marked positive effect on the course of urbanization. Our research findings show that provided grain production or grain security is guaranteed, developing countries may adopt a policy of importing an appropriate amount of grain to increase their level of urbanization. 相似文献
64.
康健 《北京市财贸管理干部学院学报》2011,(4):20-23
分析了首都粮食流通体系的现状及问题,提出了建设首都粮食流通聚集区的设想,开展了必要性分析、立地与规模需求分析,提出了建设思路、运作模式和运营重点。 相似文献
65.
66.
For a Boolean function
given by a Boolean formula (or a binary circuit) S we discuss the problem of building a Boolean formula (binary circuit) of minimal size, which computes the function g equivalent to
, or -equivalent to
, i.e.,
. In this paper we prove that if P NP then this problem can not be approximated with a good approximation ratio by a polynomial time algorithm. 相似文献
67.
Summary: Wald statistics in generalized linear models are asymptotically 2 distributed.
The asymptotic chi–squared law of the corresponding quadratic form shows disadvantages
with respect to the approximation of the finite–sample distribution. It is shown by means
of a comprehensive simulation study that improvements can be achieved by applying
simple finite–sample size approximations to the distribution of the quadratic form in
generalized linear models. These approximations are based on a 2 distribution with an
estimated degree of freedom that generalizes an approach by Patnaik and Pearson. Simulation studies confirm that nominal level is maintained with higher accuracy compared
to the Wald statistics. 相似文献
68.
Center and Distinguisher for Strings with Unbounded Alphabet 总被引:2,自引:0,他引:2
Consider two sets
and
of strings of length L with characters from an unbounded alphabet , i.e., the size of is not bounded by a constant and has to be taken into consideration as a parameter for input size. A closest string s* of
is a string that minimizes the maximum of Hamming1
distance(s, s*) over all string s : s
. In contrast, a farthest string t* from
maximizes the minimum of Hamming distance(t*,t) over all elements t: t
. A distinguisher of
from
is a string that is close to every string in
and far away from any string in
. We obtain polynomial time approximation schemes to settle the above problems. 相似文献
69.
Saul Blumenthal 《统计学通讯:理论与方法》2013,42(4):297-308
Let X1, X2,…,Xn be independent, indentically distributed random variables with density f(x,θ) with respect to a σ-finite measure μ. Let R be a measurable set in the sample space X. The value of X is observable if X ? (X?R) and not otherwise. The number J of observable X’s is binomial, N, Q, Q = 1?P(X ? R). On the basis of J observations, it is desired to estimate N and θ. Estimators considered are conditional and unconditional maximum likelihood and modified maximum likelihood using a prior weight function to modify the likelihood before maximizing. Asymptotic expansions are developed for the [Ncirc]’s of the form [Ncirc] = N + α√N + β + op(1), where α and β are random variables. All estimators have the same α, which has mean 0, variance σ2 (a function of θ) and is asymptotically normal. Hence all are asymptotically equivalent by the usual limit distributional theory. The β’s differ and Eβ can be considered an “asymptotic bias”. Formulas are developed to compare the asymptotic biases of the various estimators. For a scale parameter family of absolutely continuous distributions with X = (0,∞) and R = (T,∞), special formuli are developed and a best estimator is found. 相似文献
70.
丁述军 《山东农业大学学报(社会科学版)》2001,3(4):14-16
通过对我国粮食供求矛盾的系统分析,提出了我国粮食经济发展的三大目标;而要实现此目标,就必须选择适合我国国情的粮食供求调节机制--有限约束的市场均衡机制.在此基础上,提出了机制转换的条件及加快机制转换的对策. 相似文献