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The diffusion of new product or technical innovation over space is here modeled as an event‐based process in which the likelihood of the next adopter being in region r is influenced by two factors: (i) the potential interactions of individuals in r with current adopters in neighboring regions, and (ii) all other attributes of individuals in r that may influence their adoption propensity. The first factor is characterized by a logit model reflecting the likelihood of adoption due to spatial contacts with previous adopters, and the second by a logit model reflecting the likelihood of adoption due to other intrinsic effects. The resulting spatial diffusion process is then assumed to be driven by a probabilistic mixture of the two. A number of formal properties of this model are analyzed, including its asymptotic behavior. But the main analytical focus is on statistical estimation of parameters. Here it is shown that standard maximum‐likelihood estimates require large sample sizes to achieve reasonable results. Two estimation approaches are developed which yield more sensible results for small sample sizes. These results are applied to a small data set involving the adoption of a new Internet grocery‐shopping service by consumers in the Philadelphia metropolitan area. 相似文献
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The anatomy of the vertebral artery (VA) and two pathological conditions which affect it—tortuosity and aneurysm—are described. The changes which these lesions produce in the cervical vertebrae are also described and we present two cases in which these changes have been found. One case is of a female aged at least 45 years at the time of death from a 15th century medieval cemetery site in Britain with what we consider to be tortuosity of the VA. The second case is of a male aged between 25 and 35 years at the time of death from a Coffin period site in Japan, dating to ca 1600 years BP. The changes in this skeleton are considered to be more in keeping with a diagnosis of aneurysm of the VA. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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In human skeletons from archaeological sites, osteoarthritis is by far the most common disease found, but no case of erosive osteoarthritis has been described and we present here what we believe to be the first such case. 相似文献
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The Implementation of Controversial Facility-Complex Programs* 总被引:1,自引:0,他引:1