Biomedical subjects

Wenqing He

Publications and source records attributed to Wenqing He.

4 recordsLinked to original sources

PubMed2006

Application of reliability coefficients in cDNA microarray data analysis.

Gene expression microarray technology has been widely used in areas such as human cancer research to identify molecular characteristics of sample specimens. The microarray study, however, is a very complicated procedure which involves numerous sources of variability that may be either systematic or random. Systematic variation is often eliminated by applying normalization procedures, but at present there are no standard criteria available to evaluate the performance of a particular normalization approach. In this paper, we propose a reliability-type coefficient as a criterion to assess the effectiveness of normalization procedures in eliminating systematic variation. Simulation studies show that this criterion performs reasonably well in a range of settings. The proposed method is illustrated using a subset of an ongoing microarray study of soft-tissue sarcoma.

Computer Simulation↗

PubMed2005

[Main affecting factors of soil wind erosion under different land use patterns--a case study in Wuchuan County, Inner Mongolia].

Field investigation, laboratory analysis and wind tunnel simulation showed that in Wuchuan County of Inner Mongolia, low precipitation, frequent and high wind velocity, coarse soil texture, and thawing and freezing were the main causes of soil wind erosion happened very easily in spring. In late winter and early spring, the vegetation coverage was in order of shrub-land>natural grassland>rainfed farmland, and thus, increasing the surface cover of rainfed farmland should be an urgent need to control the wind erosion in Wuchuan County. The soil wind erosion rate decreased exponentially with increasing soil moisture content, and 6% soil moisture content was a turning point from severe to light. The topsoil moisture content under different land use patterns was in order of natural grassland> rainfed farmland >shrub-land. With increasing wind velocity, soil wind erosion rate increased by power function, and 18 m x s(-1) wind velocity was a switching point to aggravate the wind erosion.

China↗

PubMed2004

A spline function approach for detecting differentially expressed genes in microarray data analysis.

MOTIVATION: A primary objective of microarray studies is to determine genes which are differentially expressed under various conditions. Parametric tests, such as two-sample t-tests, may be used to identify differentially expressed genes, but they require some assumptions that are not realistic for many practical problems. Non-parametric tests, such as empirical Bayes methods and mixture normal approaches, have been proposed, but the inferences are complicated and the tests may not have as much power as parametric models. RESULTS: We propose a weakly parametric method to model the distributions of summary statistics that are used to detect differentially expressed genes. Standard maximum likelihood methods can be employed to make inferences. For illustration purposes the proposed method is applied to the leukemia data (training part) discussed elsewhere. A simulation study is conducted to evaluate the performance of the proposed method.

Algorithms↗

PubMed2003

Flexible maximum likelihood methods for bivariate proportional hazards models.

This article presents methodology for multivariate proportional hazards (PH) regression models. The methods employ flexible piecewise constant or spline specifications for baseline hazard functions in either marginal or conditional PH models, along with assumptions about the association among lifetimes. Because the models are parametric, ordinary maximum likelihood can be applied; it is able to deal easily with such data features as interval censoring or sequentially observed lifetimes, unlike existing semiparametric methods. A bivariate Clayton model (1978, Biometrika 65, 141-151) is used to illustrate the approach taken. Because a parametric assumption about association is made, efficiency and robustness comparisons are made between estimation based on the bivariate Clayton model and "working independence" methods that specify only marginal distributions for each lifetime variable.

Analysis of Variance↗