Robust Henderson III estimators of variance components in the nested error model

Common methods for estimating variance components in Linear Mixed Models include Maximum Likelihood (ML) and Restricted Maximum Likelihood (REML). These methods are based on the strong assumption of multivariate normal distribution and it is well know that they are very sensitive to outlying observations with respect to any of the random components. Several robust altematives of these methods have been proposed (e.g. Fellner 1986, Richardson and Welsh 1995). In this work we present several robust alternatives based on the Henderson method III which do not rely on the normality assumption and provide explicit solutions for the variance components estimators. These estimators can later be used to derive robust estimators of regression coefficients. Finally, we describe an application of this procedure to small area estimation, in which the main target is the estimation of the means of areas or domains when the within-area sample sizes are small

Comparison of doctor and patient assessments of asthma control

INTRODUCTION: The objective of asthma management is to control the condition. However, world-wide surveys reveal that only 5% of asthmatics are well controlled. One reason for this phenomenon is the fact that patients and doctors consistently over-estimate control. This study compared patient and doctor assessment of asthma control. METHODS: A random sample of asthmatics was identified by practitioners in South Africa. Patients completed an Asthma Control Test (ACT) and provided a list of medications currently being taken. The doctor also provided an assessment of control which was summarised into the categories - ’not controlled’ and ’controlled’ and listed all medications prescribed. RESULTS: The mean ACT score was 12.8 where doctors assessed the patients as being ‘not controlled’ and 20.7 where doctors assessed the patients as being ‘controlled’. Half of the patients classified themselves as being ‘not controlled’ (ACT score <20, category 1), while doctors classified only 33% of patients as being ‘not controlled’. Although only 7% of patients disagreed with the doctor’s classification of ‘not controlled’, 29% disagreed with the doctor’s assessment of being ‘controlled’. There was a significant difference in ACT score between the sexes (p < 0.0001). Most therapeutic interventions (with the exception of combination products [ICS þ LABA]) performed poorly with regard to level of control. CONCLUSION: This study suggests that asthma still appears to be relatively poorly controlled in South Africa, although levels of patient control appear to have improved compared to previous surveys, and confirms that physicians and patients differ in their assessments of asthma control.The study was funded by an unrestricted financial grant from Glaxo SmithKline

Weighting of household survey data: A comparison of various calibration, integrated and cosmetic estimators

This paper compares the bias and efficiencies of different estimation techniques aimed at creating a unique set of case weights, which can be used to estimate characteristics for both person and household variables in a household sampling survey. The resulting estimates are compatible with external population information and thus attempt to correct for differential non-response (i.e. under-representation of certain parts of the population). The existing techniques of calibration and integrated weighting and cosmetic estimators are combined and modified to give improved weighted estimators. The theoretical properties of these estimators are outlined, and the performance of the estimators is investigated via simulation studies and by application to a data set. The effect of using auxiliary information on persons only, or on both persons and households, is evaluated. The performance of the estimators under condition of differential non-response has been simulated by using unequal probability sampling to mimic such conditions.Articl

Effects of suboptimal intrauterine growth on preterm infants between 30 and 32 weeks' gestation

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The optimality of the centroid method

principal component analysis,

How do firms learn to make acquisitions?: a review of past research and an agenda for the future

How do firms learn to successfully acquire other firms? The authors first review early work, mostly from the 1980s to the mid-1990s, testing the learning curve perspective on acquisitions and exploring some contingencies. They then discuss three more recent streams of research on negative experience transfer, deliberate learning mechanisms, and learning from others, which provide deeper insight into the contingencies and mechanisms of organizational learning in strategic settings such as acquisitions. The article concludes with an agenda for future research