Calibrating longitudinal models of residential mobility and migration: an assessment of a non-parametric marginal likelihood approach

"This paper discusses the problems of controlling for omitted variables in estimating the structural parameters of longitudinal models and focuses upon an assessment of a non-parametric marginal maximum likelihood approach suggested by the results of Laird....The approach is shown to be statistically valid for a plausible discrete-time model of the incidence of residential or migration moves, at least for data in which no household moves in every time period. Empirical evaluation with two large [U.S.] datasets on residential mobility indicates that the approach is also computationally feasible and provides a promising alternative to more conventional methods for controlling for omitted variables."     

世界第一流的森林国家之一——加拿大的几点经验教训

加拿大有林地面积440万平方公里,森林覆盖率44％,相当于美国的1.5倍。尽管如此,加拿大每年生产工业用材仅1.5亿立方米,而美国是3.4亿立方米。加拿大森林生长量大约是1960万立方米,而美国的森林生长量是2010万立方米。加拿大针叶林生长量约占全国森林生长量的80％,大部分是针枞标,黑树胶、白树胶原始林,还有花旗松林、白冷杉林、雪松林、槭树林等。     

Nursing subunit technology: a replication

Overton, Schneck, and Hazlett's (1977) measurement of nursing subunit technology was replicated using 157 subunits of 9 types located in 24 hospitals in Alberta. A 21-item questionnaire was given to nurses, and the answers were subjected to factor analyses. Results indicated three dimensions of technology: instability, uncertainty, and variability. Because of the similarity of these variables to those in the Overton, Schneck, and Hazlett study, the results suggested a high degree of construct validity for the measure. The technological dimensions also differentiated among the types of subunits in the same pattern as in the original study. A relatively quick method of obtaining measures of instability, uncertainty, and variability by using composite scores was tested and found reliable.     

当前美国的各种指数简介

一、价格指数1.价比某商品若干年后的价格与其最初价格之比率。让我们通过编制食品价格指数来加以说明。假定国民的食品只由表1中所列的牛排、胡椒和面包三个项目构成,最初价格用P₀表示,七年后的价格用尸P₁表示,它们的价比P₁/P₀（100）如下:     

未来林业的准备

过去的十五年里,林业工作者受到了来自世界银行、联合国粮农组织、国际环境组织及其它有关机构研究报告的严峻挑战,这些报告不断地告诫人们,世界人口的增长,需求的提高将会对现有森林造成巨大的压力,倘若这种趋势持续下去,目前的森林管理水平将很难满足人类不断增长的需求。这些报告指出:世界人口在1975年大约是40亿,