科技期刊质量综合评价的主成分分析法及其改进

应用主成分分析进行理工大学、工业综合类科技期刊质量综合评价,根据主成分累计贡献值确定主成分的有效维数和权重,消除由于指标间的相关性带来的偏差和人为确定指标权重引起的缺陷,使评价结果更客观、公正和准确。研究了评价指标数、期刊种类数等对评价结果的影响,从而确定了合理的评价指标,得到了可靠、有效的评价结果。在18个指标中,根据保留具有重要作用变量的原则,最终选定14个有效评价指标,并且对期刊质量都具有正向作用,其中引用刊教、学科扩散指标等5个指标最重要,而影响因子的重要性最低。     

Permutational tests for correlation matrices

Permutational tests are proposed for the hypotheses that two population correlation matrices have common eigenvectors, and that two population correlation matrices are equal. The only assumption made in these tests is that the distributional form is the same in the two populations; they should be useful as a prelude either to tests of mean differences in grouped standardised data or to principal component investigation of such data.The performance of the permutational tests is subjected to Monte Carlo investigation, and a comparison is made with the performance of the likelihood-ratio test for equality of covariance matrices applied to standardised data. Bootstrapping is considered as an alternative to permutation, but no particular advantages are found for it. The various tests are applied to several data sets.     

A statistical model of tracking

A method is proposed to model individual patterns of growth over time by linear combinations of optimally chosen weighted orthogonal vectors. The goal is to distinguish individuals who track from nontrackers. Nontrackers are defined as those who follow different, usually more complex, growth patterns than trackers. Thus, nontrackers require more vectors than do trackers in modeling their longitudinal observations. A method of specifying the class-specific vectors and individual weights is demonstrated. When the proportion of nontrackers in the population is small, a modified form of the Akaike maximum entropy criterion is used to select the number of vectors appopriate for each person and also to classify each person into a tracking category. When the proportion of nontrackers is large, the modified Akaike criterion together with scatterplots of the growth curve weights are needed to distinguish trackers from nontrackers. The apprach is illustrated with longitudinal observations of height measured in an epidemiologic survey of children.