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Marginal Analysis (marginal + analysis)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Marginal Analysis of Incomplete Longitudinal Binary Data: A Cautionary Note on LOCF Imputation

BIOMETRICS, Issue 3 2004
Richard J. Cook
Summary In recent years there has been considerable research devoted to the development of methods for the analysis of incomplete data in longitudinal studies. Despite these advances, the methods used in practice have changed relatively little, particularly in the reporting of pharmaceutical trials. In this setting, perhaps the most widely adopted strategy for dealing with incomplete longitudinal data is imputation by the "last observation carried forward" (LOCF) approach, in which values for missing responses are imputed using observations from the most recently completed assessment. We examine the asymptotic and empirical bias, the empirical type I error rate, and the empirical coverage probability associated with estimators and tests of treatment effect based on the LOCF imputation strategy. We consider a setting involving longitudinal binary data with longitudinal analyses based on generalized estimating equations, and an analysis based simply on the response at the end of the scheduled follow-up. We find that for both of these approaches, imputation by LOCF can lead to substantial biases in estimators of treatment effects, the type I error rates of associated tests can be greatly inflated, and the coverage probability can be far from the nominal level. Alternative analyses based on all available data lead to estimators with comparatively small bias, and inverse probability weighted analyses yield consistent estimators subject to correct specification of the missing data process. We illustrate the differences between various methods of dealing with drop-outs using data from a study of smoking behavior. [source]

The cost of quality improvements due to integrated management of childhood illness (IMCI) in Uganda

HEALTH ECONOMICS, Issue 1 2008
David Bishai
Abstract The goal of this paper is to measure the marginal change in facility-level costs of medical care for children under five due to an increase in service quality achieved through the integrated management of childhood illness (IMCI) strategy. Since the beneficial effects of IMCI training on child health outcomes are due to IMCI's effects on service quality, costs of IMCI are regressed against measures of service quality in this paper. Our model shows that quality, as measured by a WHO-index of integrated child assessment is 44% higher in facilities with at least one health worker trained in IMCI as compared to facilities with no health workers trained in IMCI, adjusting for facility utilization as well as type of facility ownership. Our marginal analysis that tied IMCI training to quality and quality to costs shows that on the margin, investing in IMCI training at a primary facility level can yield a significant 44.3% improvement in service quality for a modest 13.5% increase in annual facility costs. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Economic analysis of different options in integrated pest and soil fertility management in maize systems of Western Kenya

AGRICULTURAL ECONOMICS, Issue 5 2010
Hugo De Groote
Abstract The major biotic constraints to the production of maize, the major staple food in Western Kenya, are field pests such as,Striga,and stem borers, and low soil fertility. To counter these constraints, new cropping systems have been developed, including "push-pull," rotations with promiscuous soybean varieties and green manure crops, and imidazolinone resistant- (IR-) maize. To analyze the technical and economic performance of these technologies, both with and without fertilizer, on-farm researcher-managed long-term trials were implemented over six seasons in two sites each in Vihiga and Siaya districts of Western Kenya. The economic results, based on marginal analysis using a multioutput, multiperiod model, show that the new cropping systems with fodder intercropping (push-pull) or soybean rotations were highly profitable. Push-pull is more profitable but requires a relatively high initial investment cost. Green manure rotation, IR-maize, and fertilizer all increased yields, but these investments were generally not justified by their increased revenue. We argue that research on rotation and cropping systems to tackle pest and soil fertility problems in Africa deserve more attention. This will require increased collaboration between agronomists and economists to set up long-term experiments with new cropping systems to develop proper economic models. [source]

USE OF COMMUNITY HEALTH NEEDS ASSESSMENT FOR REGIONAL PLANNING IN COUNTRY SOUTH AUSTRALIA

AUSTRALIAN JOURNAL OF RURAL HEALTH, Issue 1 2001
Jeff Fuller
ABSTRACT: This study examined the impact of community health needs assessments used in country South Australian health service planning between 1995 and 1999. Data were collected from regional health planning officers during a Search Conference and a series of Delphi rounds. The needs assessments were found to vary from regionally to locally driven approaches. Locally driven approaches ensured local involvement but the process was slower and required more effort from the planner. It was also felt that locally driven approaches could exacerbate tension between a community's imperatives and the regional focus of regional decision-makers. In the overall regional budgets, the reallocation of health service funds according to the needs assessment findings was only small because of difficulties in refocusing from traditional clinical services in the short term. In contrast, the impact on health service thinking about population health issues was thought to have been more significant, for example, in the development of regional women's health plans. The use of community health needs assessments was useful, but for greater impact these should not now be so ,broad-brushed', but be more focused on feasible changes that health services could support. Other priority-setting techniques, such as marginal analysis, should also be used to determine where maximum health gains can be obtained. [source]