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The effects of spatial autoregressive dependencies on inference in ordinary least squares: a geometric approach 总被引：1，自引：1，他引：0
There is a common belief that the presence of residual spatial autocorrelation in ordinary least squares (OLS) regression
leads to inflated significance levels in beta coefficients and, in particular, inflated levels relative to the more efficient
spatial error model (SEM). However, our simulations show that this is not always the case. Hence, the purpose of this paper
is to examine this question from a geometric viewpoint. The key idea is to characterize the OLS test statistic in terms of
angle cosines and examine the geometric implications of this characterization. Our first result is to show that if the explanatory
variables in the regression exhibit no spatial autocorrelation, then the distribution of test statistics for individual beta
coefficients in OLS is independent of any spatial autocorrelation in the error term. Hence, inferences about betas exhibit all the optimality properties of
the classic uncorrelated error case. However, a second more important series of results show that if spatial autocorrelation
is present in both the dependent and explanatory variables, then the conventional wisdom is correct. In particular, even when
an explanatory variable is statistically independent of the dependent variable, such joint spatial dependencies tend to produce
“spurious correlation” that results in over-rejection of the null hypothesis. The underlying geometric nature of this problem
is clarified by illustrative examples. The paper concludes with a brief discussion of some possible remedies for this problem. 相似文献
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Guo-Xiong Mei Jian-Hua Yin Jin-Min Zai Zong-Ze Yin Xiao-Li Ding Guo-Fu Zhu Lok Man Chu 《国际地质力学数值与分析法杂志》2004,28(2):111-129
This paper presents a finite layer procedure for Biot's consolidation analysis of layered soils using a cross-anisotropic elastic constitutive model. The program is first verified using published results. Then, using this program, the influences of cross-anisotropy on the immediate settlement, the final settlement, and the consolidation behaviour are investigated by changing one model parameter at one time. The results obtained using the cross-anisotropic elastic model are compared with results using an isotropic elastic model. It is found that the cross-anisotropy has very large influences on the immediate settlement, the final settlement, and the consolidation behaviour. Curves or tables of the immediate settlement coefficients, the final settlement coefficients, and the average degree of consolidation are obtained and presented in the paper. These curves or tables can be easily used to estimate the immediate settlement, the final settlement, and the consolidation settlement of a cross-anisotropic soil. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Ka Lok Li Ólafur Gudmundsson Ari Tryggvason Reynir Bödvarsson Bryndís Brandsdóttir 《Journal of Seismology》2016,20(3):771-786
Seismicity is generally concentrated on faults or in fault zones of varying, sometimes complex geometry. An earthquake catalog, compiled over time, contains useful information about this geometry, which can help understanding the tectonics of a region. Interpreting the geometrical distribution of events in a catalog is often complicated by the diffuseness of the earthquake locations. Here, we explore a number of strategies to reduce this diffuseness and hence simplify the seismicity pattern of an earthquake catalog. These strategies utilize information about event locations contained in their overall catalog distribution. They apply this distribution as an a priori constraint on relocations of the events, or as an attractor for each individual event in a collapsing scheme, and thereby focus the locations. The latter strategy is not a relocation strategy in a strict sense, although event foci are moved, because the movements are not driven by data misfit. Both strategies simplify the seismicity pattern of the catalog and may help to interpret it. A synthetic example and a real-data example from an aftershock sequence in south west Iceland are presented to demonstrate application of the strategies. Entropy is used to quantify their effect. 相似文献
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Health damages from air pollution in China 总被引：1，自引：0，他引：1
Kira Matus Kyung-Min Nam Noelle E. Selin Lok N. Lamsal John M. Reilly Sergey Paltsev 《Global Environmental Change》2012,22(1):55-66
This study evaluates air pollution-related health impacts on the Chinese economy by using an expanded version of the Emissions Prediction and Policy Analysis model. We estimated that marginal welfare impact to the Chinese economy of ozone and particulate-matter concentrations above background levels increased from 1997 US$22 billion in 1975 to 1997 US$112 billion in 2005, despite improvements in overall air quality. This increase is a result of the growing urban population and rising wages that thus increased the value of lost labor and leisure. In relative terms, however, welfare losses from air pollution decreased from 14% of the historical welfare level to 5% during the same period because the total size of the economy grew much faster than the absolute air pollution damages. In addition, we estimated that particulate-matter pollution alone led to a gross domestic product loss of 1997 US$64 billion in 1995. Given that the World Bank's comparable estimate drawn from a static approach was only 1997 US$34 billion, this result suggests that conventional static methods neglecting the cumulative impact of pollution-caused welfare damage are likely to underestimate pollution-health costs substantially. However, our analysis of uncertainty involved in exposure–response functions suggests that our central estimates are susceptible to significantly large error bars of around ±80%. 相似文献
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Dynamic Characteristics of Granite Subjected to Intermediate Loading Rate 总被引：29，自引：11，他引：18
Summary A large diameter split Hopkinson pressure bar (SHPB) has been developed. This equipment is briefly described, together with a shaped striker that initiates a half-sine incident waveform to obtain the complete stress-strain relationship of the Bukit Timah granite at medium strain rate. Good constant strain rate was derived, and the dynamic complete stress-strain curves and energy absorption of the granite were measured at a strain rate between 20 and 60 per second. Repeated impact between 60–90% of the static strength of the granite was also conducted. Results from the tests show that the cumulative damage of the granite depends on the peak stress of the dynamic loads with a fixed duration. The dynamic fracture strength of the granite loaded at medium strain rate is directly proportional to the cube root of the strain rate. For the granite loaded at this strain rate, Youngs modulus is unchanged. Energy absorption of the samples loading to fragmentation determined its fragmented size distribution. At high strain rate, the rock possesses large energy absorption and the particle size of the fragments is much smaller. 相似文献
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2008年5月12日汶川MS8.0地震主震发生后至2012年5月12日,我国地震台网在龙门山断裂区域内（102°E-105°E,30°N-34°N）共记录93837个地震事件,其中80995次事件含有深度信息.本文以台网地震目录为主要研究对象,分析了汶川地震余震序列的时空分布与演化特征.与构造活动密切相关的余震频次-震级关系变化显示,与主震断裂活动直接相关的余震活动在主震后4个月内基本结束.余震释放能量的空间分布及演化分析显示,在主震后6~24 h即有可能捕获未来余震区的大致展布乃至余震发展趋势. 相似文献
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X. Li T. S. Lok D. A. Summers G. Rupert J. Tyler 《Geotechnical and Geological Engineering》2001,19(2):119-136
Experiments have been conducted using an impact method with drop-hammers to obtain the required signals so that a detailed analysis of these data could be undertaken to quantify the drillability index of rocks. The dynamic stress waveform or reflected energy from the rock-drill bit interface is represented as a drillability index. This information enables the assessment of the characteristics of the rock under the bit. The results show that neither the amplitude nor the frequency spectra of the reflected stress wave significantly changes with the type of rock tested. However, the energy reflection coefficient varies with rock hardness. In the process of drilling the rocks, the energy reflection coefficient can increase by approximately 20% when the hardness or penetration resistance index of rock is doubled. This investigation confirmed the variation of reflected energy of rocks. For a single sharp or domed indentor, energy reflection decreases with penetration resistance index of the rock while it increases with this index in actual drilling or testing of percussive bits. In drill bit design and in tests for using a single indentor, a reasonable indentor shape should be adopted to correspond to a high energy reflection coefficient. By contrast, the energy reflection from a drill system or percussive bit should be minimised in practice. 相似文献