Models for the analysis of C-reactive protein in statin trials

Elevation in C-reactive protein (CRP) is an independent risk factor for cardiovascular disease progression and levels are reduced by treatment with statins. However, on-treatment CRP, given baseline CRP and treatment, is not normally distributed and outliers exist even when transformations are applied. Although classical non-parametric tests address some of these issues, they do not enable straightforward inclusion of covariate information. The aims of this study were to produce a model that improved efficiency and accuracy of analysis of CRP data. Estimation of treatment effects and identification of outliers were addressed using controlled trials of rosuvastatin. The robust statistical technique of MM-estimation was used to fit models to data in the presence of outliers and was compared with least-squares estimation. To develop the model, appropriate transformations of the response and baseline variables were selected. The model was used to investigate how on-treatment CRP related to baseline CRP and estimated treatment effects with rosuvastatin. On comparing least-squares and MM-estimation, MM-estimation was superior to least-squares estimation in that parameter estimates were more efficient and outliers were clearly identified. Relative reductions in CRP were higher at higher baseline CRP levels. There was also evidence of a dose-response relationship between CRP reductions from baseline and rosuvastatin. Several large outliers were identified, although there did not appear to be any relationships between the incidence of outliers and treatments. In conclusion, using robust estimation to model CRP data is superior to least-squares estimation and non-parametric tests in terms of efficiency, outlier identification and the ability to include covariate information.     

IMPROVING POPULATION-SPECIFIC ALLELE FREQUENCY ESTIMATES BY ADAPTING SUPPLEMENTAL DATA: AN EMPIRICAL BAYES APPROACH

Estimation of the allele frequency at genetic markers is a key ingredient in biological and biomedical research, such as studies of human genetic variation or of the genetic etiology of heritable traits. As genetic data becomes increasingly available, investigators face a dilemma: when should data from other studies and population subgroups be pooled with the primary data? Pooling additional samples will generally reduce the variance of the frequency estimates; however, used inappropriately, pooled estimates can be severely biased due to population stratification. Because of this potential bias, most investigators avoid pooling, even for samples with the same ethnic background and residing on the same continent. Here, we propose an empirical Bayes approach for estimating allele frequencies of single nucleotide polymorphisms. This procedure adaptively incorporates genotypes from related samples, so that more similar samples have a greater influence on the estimates. In every example we have considered, our estimator achieves a mean squared error (MSE) that is smaller than either pooling or not, and sometimes substantially improves over both extremes. The bias introduced is small, as is shown by a simulation study that is carefully matched to a real data example. Our method is particularly useful when small groups of individuals are genotyped at a large number of markers, a situation we are likely to encounter in a genome-wide association study.     

州权与外交政策——外交权力应交由华府

与其他国家相比,美国的州和地方政府享有极大的自主权,甚至可以自行对外实施制裁,他们无视联邦政府的对外政策,擅自把许多国家纳入自己的制裁范围,不仅使美国在外交事务上不能“以一个声音说话”,还给从事国际贸易的美国企业带来了实际的经济损失。针对州和地方政府有无权力制定自己的对外政策,文章从法律的角度进行了探讨。     

当心经济险滩!——试析美、日、欧经济的前景与影响

世界经济正减速。美国在经历了近10年的持续有力的增长之后,发展速度显著下降。欧洲也是如此,疲态已尽显无遗,日本经济10年来毫无起色。如此看来,我们是否在走向衰退或金融危机?我们将如何应对?     

学龄儿童健康行为研究方法述评

学龄儿童健康行为研究越来越得到重视,在未来周期性的研究中也面临着在快速发展的背景下保持较高质量、在有限的财政资源情况下持续提高、使趋势分析与修改问卷内容相适应、满足科学受众和政策受众的不同要求等挑战,因此,完善其研究方法成为当前迫切需要。     

第七届应用语言学国际会议

如果认真考察决定某种新学术流派发展的基本趋势,就可以发现这种趋势的特点存在两种直接对立的现象:一是企图依靠划分新的研究领域而成为一门独立的学科;二是在传统的各科之间产生的边缘学科力求使之一体化。现代应用语言学的研究对象及其完整的概念、术语、方法、目的和发展远景,十分明显地在国际应用语言学会所举办的历次会议上显示出来。第七届应用语言学例行国际会议,是国际应用     

Comparing two survey methods for estimating maternal and perinatal mortality in rural Cambodia

PURPOSE: We need solid estimates of maternal mortality rates (MMR) to monitor the impact of maternal care programs. Cambodian health authorities and WHO report the MMR in Cambodia at 450 per 100,000 live births. The figure is drawn from surveys where information is obtained by interviewing respondents about the survival of all their adult sisters (sisterhood method). The estimate is statistically imprecise, 95% confidence intervals ranging from 260 to 620/100,000. The MMR estimate is also uncertain due to under-reporting; where 80-90% of women deliver at home maternal fatalities may go undetected especially where mortality is highest, in remote rural areas. The aim of this study was to attain more reliable MMR estimates by using survey methods other than the sisterhood method prior to an intervention targeting obstetric rural emergencies. PROCEDURES: The study was carried out in rural Northwestern Cambodia where access to health services is poor and poverty, endemic diseases, and land mines are endemic. Two survey methods were applied in two separate sectors: a community-based survey gathering data from public sources and a household survey gathering data direct from primary sources. FINDINGS: There was no statistically significant difference between the two survey results for maternal deaths, both types of survey reported mortality rates around the public figure. The household survey reported a significantly higher perinatal mortality rate as compared to the community-based survey, 8.6% versus 5.0%. Also the household survey gave qualitative data important for a better understanding of the many problems faced by mothers giving birth in the remote villages. There are detection failures in both surveys; the failure rate may be as high as 30-40%. PRINCIPLE CONCLUSION: Both survey methods are inaccurate, therefore inappropriate for evaluation of short-term changes of mortality rates. Surveys based on primary informants yield qualitative information about mothers' hardships important for the design of future maternal care interventions.     

Multiparous women's confidence to have a publicly-funded homebirth: a qualitative study

Background

Hospital birth is commonly thought to be a safer option than homebirth, despite many studies showing similar rates of safety for low risk mothers and babies when cared for by qualified midwives with systems of back-up in place. Recently in Australia, demand has led to the introduction of a small number of publicly-funded homebirth programs. Women's confidence in having a homebirth through a publicly-funded homebirth program in Australia has not yet been explored.

Aim

The aim of the study was to explore the reasons why multiparous women feel confident to have a homebirth within a publicly-funded model of care in Australia.

Methods

Ten multiparous English-speaking women who chose to have a homebirth with the St George Hospital Homebirth Program were interviewed in the postnatal period using semi-structured, open-ended questions. Interviews were transcribed, then a thematic analysis was undertaken.

Results

Women, having already experienced a normal birth, demonstrated a strong confidence in their ability to give birth at home and described a confidence in their bodies, their midwives, and the health system. Women weighed up the risks of homebirth through information they gathered and integration with their previous experience of birth, their family support and self-confidence.

Discussion

Women choosing publicly-funded homebirth display strong confidence in both themselves to give birth at home, and their belief in the health system's ability to cope with any complications that may arise.

Implications for practice

Many women may benefit from access to publicly-funded homebirth models of care. This should be further investigated.     

Estimating the Effect of the One-Child Policy on the Sex Ratio Imbalance in China: Identification Based on the Difference-in-Differences

In China, the male-biased sex ratio has increased significantly. Because the one-child policy applies only to the Han Chinese but not to minorities, this unique affirmative policy allows us to identify the causal effect of the one-child policy on the increase in sex ratios by using a difference-in-differences (DD) estimator. Using the 1990 census, we find that the strict enforcement of the one-child policy led to 4.4 extra boys per 100 girls in the 1980s, accounting for about 94% of the total increase in sex ratios during this period. The robust tests indicate that the estimated policy effect is not likely confounded by other omitted policy shocks or socioeconomic changes. Moreover, we conduct the DD estimation using both the 2000 census and the 2005 mini-census. Our estimates suggest that the one-child policy resulted in about 7.0 extra boys per 100 girls for the 1991–2005 birth cohorts. The effect of the one-child policy accounts for about 57% and 54% of the total increases in sex ratios for the 1991–2000 and 2001–2005 birth cohorts, respectively.