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It is often the case that high-dimensional data consist of only a few informative components. Standard statistical modeling and estimation in such a situation is prone to inaccuracies due to overfitting, unless regularization methods are practiced. In the context of classification, we propose a class of regularization methods through shrinkage estimators. The shrinkage is based on variable selection coupled with conditional maximum likelihood. Using Stein's unbiased estimator of the risk, we derive an estimator for the optimal shrinkage method within a certain class. A comparison of the optimal shrinkage methods in a classification context, with the optimal shrinkage method when estimating a mean vector under a squared loss, is given. The latter problem is extensively studied, but it seems that the results of those studies are not completely relevant for classification. We demonstrate and examine our method on simulated data and compare it to feature annealed independence rule and Fisher's rule.  相似文献   
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We consider the problem of approximate sorting of a data stream (in one pass) with limited internal storage where the goal is not to rearrange data but to output a permutation that reflects the ordering of the elements of the data stream as closely as possible. Our main objective is to study the relationship between the quality of the sorting and the amount of available storage. To measure quality, we use permutation distortion metrics, namely the Kendall tau, Chebyshev, and weighted Kendall metrics, as well as mutual information, between the output permutation and the true ordering of data elements. We provide bounds on the performance of algorithms with limited storage and present a simple algorithm that asymptotically requires a constant factor as much storage as an optimal algorithm in terms of mutual information and average Kendall tau distortion. We also study the case in which only information about the most recent elements of the stream is available. This setting has applications to learning user preference rankings in services such as Netflix, where items are presented to the user one at a time.  相似文献   
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In this article, we propose a new product positioning method based on the neural network methodology of a self‐organizing map. The method incorporates the concept of rings of influence, where a firm evaluates individual consumers and decides on the intensity to pursue a consumer, based on the probability that this consumer will purchase a competing product. The method has several advantages over earlier work. First, no limitations are imposed on the number of competing products and second, the method can position multiple products in multiple market segments. Using simulations, we compare the new product positioning method with a quasi‐Newton method and find that the new method always approaches the best solution obtained by the quasi‐Newton method. The quasi‐Newton method, however, is dependent on the initial positions of the new products, with the majority of cases ending in a local optimum. Furthermore, the computational time required by the quasi‐Newton method increases exponentially, while the time required by the new method is small and remains almost unchanged, when the number of new products positioned increases. We also compute the expected utility that a firm will provide consumers by offering its products. We show that as the intensity with which a firm pursues consumers increases, the new method results in near‐optimal solutions in terms of market share, but with higher expected utility provided to consumers when compared to that obtained by a quasi‐Newton method. Thus, the new method can serve as a managerial decision‐making tool to compare the short‐term market share objective with the long‐term expected utility that a firm will provide to consumers, when it positions its products and intensifies its effort to attract consumers away from competition.  相似文献   
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The aim of this study was to explore the relations between gambling, brain emotion systems, personality, self/other perception, and hopelessness in an Italian community. Dimensions of gambling, positive and negative emotions, self/other perception, personality and hopelessness were assessed in a community sample of 235 adults aged 19–59 years. Two structural models were tested. We found a significant correlation between problem gambling and impulsivity, which in association with aggressivity and negative personality dimensions may help explain the psychopathology factor, i.e. a latent variable involving neurotic personality, hopelessness, high sensation seeking, low metacognitive responsiveness, and disorganized patterns of interpersonal relationships. These results contribute to develop a theoretical framework of gambling in relation with personality factors and provide a new approach for clinical intervention of problem gambling that relies on a solid multidimensional perspective.  相似文献   
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Social movement scholars have suggested that opportunity structures are not objective features of the world but must be constructed by social forces, including social movements. Here, we attempt to analyze how Palestinians living in the occupied territories constructed political opportunity during the run-up to the 1987 first Intifada. We analyze how the changing Israeli political opportunity structure affected Palestinians’ framing of the structural conditions they faced. In particular, we examine (1) how the consolidating Palestinian movement within the occupied territories built the capacity for a shared, collective framing of events, and (2) how the movement adapted a strategy based on its understanding of the opportunity presented by divisions in Israeli society concerning the occupation. Based on the analysis, we offer several insights into the Intifada's dynamics and trajectories.
Eitan Y. AlimiEmail:
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This study compares the health status and survival of the elderly in two countries, Italy and Israel. While both are developed Mediterranean countries, their degree of ageing, characteristic features of the elderly, health status and survival are different. The data are from two sample surveys and, for Israel, from a record linkage between survey and mortality data at five years remove. A preliminary analysis, using a multiple correspondence factorial analysis, highlighted a gradual change in living arrangements and socio-economic features as the population ages, which was only slightly associated with health conditions. In Israel, moreover, the Arab minority differs according to social conditions, living arrangements and health status. The determinants of health status and survival of the elderly in both countries were studied using as dependent variables; 1) self-perceived health status, 2) the frequency of medical examinations; 3) medical tests, for both countries and 4) (for Israel) deaths. Linear logistic models were constructed using, as explanatory variables, sex, age and living arrangements, a variable indicative of community level socio-economic and cultural conditions, two indicators describing individual socio-economic conditions and smoking habits. Thus it is possible to assess the impact of explanatory variables by comparing both subjective conditions and behaviour factors regarding medical care, with the unequivocal confirmation provided by death.  相似文献   
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