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271.
Raegen T. MILLER Richard J. MURNANE John B. WILLETT 《International labour review / International Labour Office》2008,147(1):71-89
This article studies the impact of teacher absences on education. Using data spanning three academic years about 285 teachers and 8,631 predominantly economically disadvantaged students from a United States urban school district, it tests assumptions that a substantial portion of teachers' absences is discretionary and that these absences reduce productivity – students' mathematics scores. Since absent teachers are typically replaced by less qualified substitutes, instructional intensity and consistency may decline: ten days of teacher absence reduce students' achievement score by about 3.3 per cent of a standard deviation – enough to lower some students' designation in the state proficiency system and, thus, their motivation to succeed. 相似文献
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Richard A. Lockhart John J. Spinelli Michael A. Stephens 《Revue canadienne de statistique》2007,35(1):125-133
Choulakian, Lockhart & Stephens (1994) proposed Cramér‐von Mises statistics for testing fit to a fully specified discrete distribution. The authors give slightly modified definitions for these statistics and determine their asymptotic behaviour in the case when unknown parameters in the distribution must be estimated from the sample data. They also present two examples of applications. 相似文献
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Urban tree cover: an ecological perspective 总被引:11,自引:4,他引:7
Zipperer Wayne C. Sisinni Susan M. Pouyat Richard V. Foresman Timothy W. 《Urban Ecosystems》1997,1(4):229-246
Analysis of urban tree cover is generally limited to inventories of tree structure and composition on public lands. This approach provided valuable information for resource management. However, it does not account for all tree cover within an urban landscape, thus providing insufficient information on ecological patterns and processes. We propose evaluating tree cover for an entire urban area that is based on patch dynamics. Treed patches are classified by their origin, structure, and management intensity. A patch approach enables ecologists to evaluate ecological patterns and processes for the entire urban landscape and to examine how social patterns influence these ecological patterns and processes. 相似文献
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The European region is undergoing dramatic social change. Among other regional and international forces, these changes are rooted in: the collapse of the former Soviet Union; the sudden appearance of a large number of “new” – mostly poor and politically unstable – European nations; and, the emergence of economic trading blocs in North America and Asia. At the same time, the majority of “established” European nations are experiencing sluggish rates of economic growth, moderate to high levels of inflation, high unemployment, escalating demands on public social services, and low fertility in combination with high rates of population aging and immigration from developing countries. Despite the seriousness of the dilemmas confronting the region, European development accomplishments of the past 25 years suggest that the region's leaders already possesses the resources required to solve its complex, social, political, and economic challenges. 相似文献