An information-theoretic approach to surrogate-marker evaluation with failure time endpoints

10.1007/s10985-010-9185-6Lifetime Data Analysis172195-21

Estimating negative variance components from Gaussian and non-Gaussian data: a mixed models approach

The occurrence of negative variance components is a reasonably well understood phenomenon in the case of linear models for hierarchical data, such as variance-component models in designed experiments or linear mixed models for longitudinal data. In many cases, such negative variance components can be translated as negative within-unit correlations. It is shown that negative variance components, with corresponding negative associations, can occur in hierarchical models for non-Gaussian outcomes as well, such as repeated binary data or counts. While this feature poses no problem for marginal models, in which the mean and correlation functions are modeled directly and separately, the issue is more complicated in, for example, generalized linear mixed models. This owes in part to the non-linear nature of the link function, non-constant residual variance stemming from the mean-variance link, and the resulting lack of closed-form expressions for the marginal correlations. It is established that such negative variance components in generalized linear mixed models can occur in practice and that they can be estimated using standard statistical software. Marginal-correlation functions are derived. Important implications for interpretation and model choice are discussed. Simulations and the analysis of data from a developmental toxicity experiment underscore these results. © 2010 Elsevier B.V. All rights reserved.status: publishe

Estimating negative variance components from Gaussian and non-Gaussian data: A mixed models approach

10.1016/j.csda.2010.09.002Computational Statistics and Data Analysis5521071-1085CSDA

<雜錄>新たに発見された玄奘三藏の遺骨

GP management checklist. (PDF 145 kb

Control of blood pressure and risk attenuation: a public health intervention in rural Bangladesh, Pakistan, and Sri Lanka: feasibility trial results.

BACKGROUND: High blood pressure (BP) is the leading attributable risk for cardiovascular disease globally. There is little information on effective and sustainable public health system strategies for managing hypertension in South Asian countries. We conducted a feasibility study to gather preliminary data to optimize BP-lowering strategies for a public health intervention in rural communities in Bangladesh, Pakistan, and Sri Lanka. METHODS: A mixed method feasibility study comprised a 3-month pre and postevaluation of a multicomponent intervention (MCI), including BP screening and home health education by trained government community health worker (CHW); providers trained in hypertension management, and compensation of CHW for additional services. Checklists were used to document care. Stakeholder interviews were also conducted. Individuals aged 40 years and above with high BP (systolic ≥140 mmHg or diastolic ≥90 mmHg based on two readings from 2 separate days, or receiving antihypertensive medications) were enrolled from rural communities in Bangladesh, Pakistan, and Sri Lanka. BP was measured at baseline and 3 months postintervention. RESULTS: A total of 412 (90%) of the 454 eligible individuals were recruited. Of those recruited, 90% received home health education session by trained CHWs, 80% were referred to trained providers, of whom 83% completed the management checklist. A follow-up rate of 95.6% was achieved. The mean SBP declined significantly by 4.5 mmHg 95% confidence interval (2.3, 6.7) mmHg (P \u3c 0.001) in the overall pooled analysis in three countries; however, it varied among countries. BP decline was 10.5 mmHg (8.1, 13.0 mmHg) (P \u3c 0.001) in the pooled analysis of individuals with uncontrolled hypertension at baseline, and was also significant each of the three countries. All 98 stakeholders strongly supported upscaling the proposed MCI strategies. CONCLUSION: The proposed MCI is feasible for implementation and requires long-term, large-scale evaluation in the rural public health infrastructure in South Asian countries to determine sustainability of health system changes and BP control. If these long-term effects are confirmed, MCI may be a long-term strategy for tackling rising rates of cardiovascular disease in low-resourced countries