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11.
John D. Emerson David C. Hoaglin Frederick Mosteller 《Statistical Methods and Applications》1993,2(3):269-290
Summary Meta-analyses of sets of clinical trials often combine risk differences from several 2×2 tables according to a random-effects
model. The DerSimonian-Laird random-effects procedure, widely used for estimating the populaton mean risk difference, weights
the risk difference from each primary study inversely proportional to an estimate of its variance (the sum of the between-study
variance and the conditional within-study variance). Because those weights are not independent of the risk differences, however,
the procedure sometimes exhibits bias and unnatural behavior. The present paper proposes a modified weighting scheme that
uses the unconditional within-study variance to avoid this source of bias. The modified procedure has variance closer to that
available from weighting by ideal weights when such weights are known. We studied the modified procedure in extensive simulation
experiments using situations whose parameters resemble those of actual studies in medical research. For comparison we also
included two unbiased procedures, the unweighted mean and a sample-size-weighted mean; their relative variability depends
on the extent of heterogeneity among the primary studies. An example illustrates the application of the procedures to actual
data and the differences among the results.
This research was supported by Grant HS 05936 from the Agency for Health Care Policy and Research to Harvard University. 相似文献
12.
Marzia Freo 《Statistical Methods and Applications》2005,14(2):271-281
The present paper analyses the impact of sales promotions on store performance, in the short and long term, from the retailer's
point of view. Relationships among promoted and regular sales in the hypermarkets of a large-scale retail chain of national
importance, are investigated by means of a structural vector autoregressive model (SVAR). Statistically significant effects
of sales promotions in the heavy household section on store sales are found in the short-run; these promotions produce additional
sales and thus act as an attractive factor. Promotions in textile category, on the contrary, produce an immediate negative
effect on net sales. In the long run, negative statistically significant effects on regular sales are detected when promotions
are repeatedly implemented within perishables category. 相似文献
13.
Generalized additive models for location, scale and shape 总被引:10,自引:0,他引:10
R. A. Rigby D. M. Stasinopoulos 《Journal of the Royal Statistical Society. Series C, Applied statistics》2005,54(3):507-554
Summary. A general class of statistical models for a univariate response variable is presented which we call the generalized additive model for location, scale and shape (GAMLSS). The model assumes independent observations of the response variable y given the parameters, the explanatory variables and the values of the random effects. The distribution for the response variable in the GAMLSS can be selected from a very general family of distributions including highly skew or kurtotic continuous and discrete distributions. The systematic part of the model is expanded to allow modelling not only of the mean (or location) but also of the other parameters of the distribution of y , as parametric and/or additive nonparametric (smooth) functions of explanatory variables and/or random-effects terms. Maximum (penalized) likelihood estimation is used to fit the (non)parametric models. A Newton–Raphson or Fisher scoring algorithm is used to maximize the (penalized) likelihood. The additive terms in the model are fitted by using a backfitting algorithm. Censored data are easily incorporated into the framework. Five data sets from different fields of application are analysed to emphasize the generality of the GAMLSS class of models. 相似文献
14.
教育对经济增长的抑制效应是教育对经济增长双重效应的一个重要方面。本文从确认教育对经济增长的抑制效应的存在出发,分析了教育对经济增长抑制效应的具体情形,探讨了教育对经济增长抑制效应的存在机制。 相似文献
15.
罗瑜 《重庆大学学报(社会科学版)》2005,11(1):92-95
本文通过研究各种二语习得理论对频率效应的论述及相关实证,力图探索频率效应在二语习得中的重要作用.作者认为:尽管频率不能解释所有语言学习现象,其效应却体现在二语习得的各个方面,频率应是二语习得理论不可或缺的部分. 相似文献
16.
信息产业对经济增长贡献的计量分析 总被引:3,自引:0,他引:3
文章试图对信息产业对经济增长的贡献作一定量分析。为此,首先将国内部门分为信息产业与非信息产业两大部门,并以这两部门的生产函数为基础,推导出最终的计量模型,然后根据湖北省的有关数据对模型进行回归分析。分析的结果表明,信息产业对经济增长的综合的边际产出贡献很高,从而说明对信息产业应继续加大投入,引导和扶持信息产业的发展,以促进整个湖北省经济持续、高速、稳定增长。 相似文献
17.
Kepher Henry Makambi 《Statistical Methods and Applications》2002,11(1):127-138
The standard hypothesis testing procedure in meta-analysis (or multi-center clinical trials) in the absence of treatment-by-center
interaction relies on approximating the null distribution of the standard test statistic by a standard normal distribution.
For relatively small sample sizes, the standard procedure has been shown by various authors to have poor control of the type
I error probability, leading to too many liberal decisions. In this article, two test procedures are proposed, which rely
on thet—distribution as the reference distribution. A simulation study indicates that the proposed procedures attain significance
levels closer to the nominal level compared with the standard procedure. 相似文献
18.
王金玲 《盐城师范学院学报》2002,22(4):76-78
英语“临时语”是一种偏离语言常规的“变异”(deviation)现象 ,往往产生独特的修辞效果。“临时语”的构成方法有词缀法、转化法、合成法、拼缀法、缩略法、类推法和新选七种 ,“临时语”具有简洁明快 ,加强语气 ,鲜明生动、诙谐戏谑的修辞效果 相似文献
19.
The far-reaching effects of the social systemic division of labor on the organization and contents of primary ties make the Community Question an important issue for many sociologists. This paper looks at the personal embeddedness of families in three German cities (Berlin, Hamburg, and Stuttgart) and examines the Community Question with data collected at the end of 2003. It is based on the theoretical views of Wellman [Wellman, B., 1979. The community question. The intimate networks of East Yorkers. American Journal of Sociology 84, 1201–1231], who used a network analysis perspective to conceptualize “the Community Question”. The results of this German study generally support the results of Wellman's second East York Study. However, the network structures analyzed in my study vary from the three ideal-type models. Cluster analysis shows that Wellman's typology can be replicated relatively well in Germany. In contrast to traditional discourse related to the Community Question, particular network types are not associated with low levels of social relations. Moreover, structural factors do not explain the existence of different network types. Thus, the networks are not a product of only one community model. They suggest that it is less helpful to talk about “Saved”, “Lost”, or “Liberated” communities than it is to regard communities as a mixture of strongly-knit nuclear clusters and of broader, sparsely-knit relations that provide access to different groups and their resources. 相似文献
20.
Denis Larocque 《Revue canadienne de statistique》2003,31(4):437-455
The author presents a multivariate location model for cluster correlated observations. He proposes an affine‐invariant multivariate sign statistic for testing the value of the location parameter. His statistic is an adaptation of that proposed by Randles (2000). The author shows, under very mild conditions, that his test statistic is asymptotically distributed as a chi‐squared random variable under the null hypothesis. In particular, the test can be used for skewed populations. In the context of a general multivariate normal model, the author obtains values of his test's Pitman asymptotic efficiency relative to another test based on the overall average. He shows that there is an improvement in the relative performance of the new test as soon as intra‐cluster correlation is present Even in the univariate case, the new test can be very competitive for Gaussian data. Furthermore, the statistic is easy to compute, even for large dimensional data. The author shows through simulations that his test performs well compared to the average‐based test. He illustrates its use with real data. 相似文献