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Randomized trials with dropouts or censored data and discrete time-to-event type outcomes are frequently analyzed using the Kaplan-Meier or product limit (PL) estimation method. However, the PL method assumes that the censoring mechanism is noninformative and when this assumption is violated, the inferences may not be valid. We propose an expanded PL method using a Bayesian framework to incorporate informative censoring mechanism and perform sensitivity analysis on estimates of the cumulative incidence curves. The expanded method uses a model, which can be viewed as a pattern mixture model, where odds for having an event during the follow-up interval $$({t}_{k-1},{t}_{k}]$$, conditional on being at risk at $${t}_{k-1}$$, differ across the patterns of missing data. The sensitivity parameters relate the odds of an event, between subjects from a missing-data pattern with the observed subjects for each interval. The large number of the sensitivity parameters is reduced by considering them as random and assumed to follow a log-normal distribution with prespecified mean and variance. Then we vary the mean and variance to explore sensitivity of inferences. The missing at random (MAR) mechanism is a special case of the expanded model, thus allowing exploration of the sensitivity to inferences as departures from the inferences under the MAR assumption. The proposed approach is applied to data from the TRial Of Preventing HYpertension. 相似文献
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Analysis by GC and GC/MS of the essential oil obtained from above-ground parts of Micromeria dalmatica Benth. allowed the identification of 116 components, comprising 93.6% of the total oil composition. The major compounds are 3-oxygenated p-menthane monoterpenes and were identified as pulegone (29.6%), menthone (11.7%), and piperitenone (10.8%). The chemical composition of this and additional 30 oils obtained from selected Micromeria Benth. taxa were compared by using multivariate statistical analysis (agglomerative hierarchical cluster analysis and principal component analysis (PCA)). The results of statistical analyses, as well as the domination of different concurrent p-menthane-skeleton-type monoterpene biosynthetical sub-branches in the compared M. dalmatica samples, implied the occurrence of at least two different chemotypes of the mentioned species. 相似文献
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Speybroeck N Marcotty T Aerts M Dolan T Williams B Lauer J Molenberghs G Burzykowski T Mulumba M Berkvens D 《Experimental parasitology》2008,118(4):522-530
Theileria parva is the causative agent of East Coast fever (ECF), an important cattle disease in East and Central Africa. One of the methods for control of ECF is 'infection and treatment', a procedure in which an animal is infected with the live parasite and at the same time treated with a long-acting oxytetracycline formulation, restraining the infection and allowing a protective cellular immune response to develop. Optimal immunizing doses were estimated using models of trichotomous response: dysimmunization (death or severe reaction during immunization), immunization failure (death or severe reaction during lethal challenge) and successful immunization (neither dysimmunization nor immunization failure). In this paper we present methods of interpreting immunization trials and apply these methods to previously unpublished data from two such trials: one with a mixture of three T. parva stocks and one with a single T. parva stock. We explain why titration trials conducted with a cocktail of antigens could predict a suboptimal immunization dose. Indeed it is possible for a combination of three individually efficient stocks to result in a mixture with which optimal immunization response might be difficult to achieve, because of averaging effects. The corresponding interpretation provides insights into why standard immunization trials for T. parva have not yielded the results that might be expected of them. The results of this work may also have implications for the use of antigen cocktails in cancer, HIV and malaria vaccine trials. 相似文献
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W.R.M. Aengevaeren G.J. Laarman M.J. Suttorp J.M. ten Berg A.J. van Boven M.J. de Boer J.J. Piek G.V.A. van Ommen J.G.F. Bronzwaer P. Smits J.W. Deckers 《Netherlands heart journal》2005,13(11):416-422
Interventional cardiology is an expanding field within cardiovascular medicine and today it is generally accepted that cardiologists require specific training, knowledge and skills. Hospitals where coronary interventions are performed must be properly equipped and able to provide specialised care. Percutaneous coronary interventions are frequently used for coronary revascularisation. The public should have confidence in the uniformity of high quality care. Therefore, such quality of care should be maintained by certification of the individual operators, general guidelines for institutional requirements and formal audits. The Netherlands Society of Cardiology (NVVC) will be implementing a new registration system for cardiologists with a subspecialisation that will include registration for interventional cardiology. The NVVC asked the Working Group of Interventional Cardiology (WIC) to update the 1994 Dutch guidelines on operator and institutional competence, and requirements for training in interventional cardiology in order to incorporate them into the official directives. The present guidelines represent the expert opinion of the Dutch interventional cardiology community and are in accordance with international regulations.After two rounds of discussion, the NVVC approved the guidelines in November 2004 during the autumn meeting. 相似文献
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Soils and vegetation of Angai forest: ecological insights from a participatory survey in South Eastern Tanzania 总被引:2,自引:1,他引:1
S. Dondeyne A. Wijffels L. B. Emmanuel J. Deckers M. Hermy 《African Journal of Ecology》2004,42(3):198-207
Soils and vegetation of a woodland in South Eastern Tanzania were studied in support of a project fostering community participation in the management of a proposed forest reserve. In nine sites within an area of 500 km2, soils were characterized, frequency of occurrence of woody species was assessed and diameter at breast height of timber species recorded. Villagers identified 133 species of which only 56% were scientifically identified. However, as ordination axes derived from the complete data set were highly correlated with those derived from the restricted data set, the latter could be used. On the undulating plains, deep, sandy soils (Hypoluvic Arenosols, Profondic and Arenic Luvisols) occurred low in organic carbon, exchangeable bases and extractable aluminium content. Most common canopy species were Brachystegia spiciformis/B. boehmii and Pterocarpus angolensis. On the dissected plains on shallow, clayey soils (Leptic Cambisols) with higher organic carbon, exchangeable bases and extractable aluminium content, Acacia nigrescens and Markhamia spp. were the most common tree species. On deeper, fertile clayey soils (Profondic Lixisols and Chromic Phaeozems) vegetation consisted of species found in the two vegetation groups. Pterocarpus angolensis and Pericopsis angolensis were the only valuable timber species commonly found, most frequently on the undulating plains. As soils of this area are unfavourable for agriculture, it seems sensible to set this area aside as a forest reserve. 相似文献
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Desulfovibrio vulgaris Hildenborough contains a family of genes for methyl-accepting chemotaxis proteins (MCPs). Here we report the complete sequence of the gene for Desulfovibrio chemoreceptor H (dcrH). The deduced amino acid sequence of DcrH protein, which has an enlarged N-terminal, ligand binding domain, indicates a structure similar to that of other MCPs. Comparison of the sequences for DcrA, determined earlier, and DcrH indicated that similarity is essentially limited to the C-terminal excitation region. The dcr gene family differs, in this respect, from mcp gene families in other eubacteria (e.g. Escherichia coli and Bacillus subtilis), where MCPs share significant homology throughout their C-terminal signal transduction domains. This may point to an ancient evolutionary origin of the dcr gene family, which is widely distributed throughout the genus Desulfovibrio. The evolutionary origin of mcp genes was traced by comparing nucleotide sequences for the excitation region that is common to all MCPs. Phylogenetic analysis of sequences for thirty mcp genes from nine eubacterial and one archaebacterial species suggested that multiplication of mcp genes has occurred at least twice since the eubacteria diverged from the archaebacteria.Nucleotide accession number: The nucleotide sequence reported in this paper has been entered into GenBank under accession number U30319. Phone: 403-220-6388. Fax: 403-289-9311. Electronic mail address: voordouw@acs.ucalgary.ca. 相似文献
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Joerg Latus Klara Tenner-Racz Paul Racz Daniel Kitterer Daniel Cadar German Ott M. Dominik Alscher Jonas Schmidt-Chanasit Niko Braun 《PloS one》2014,9(5)