Block-Conditional Missing at Random Models for Missing Data

Two major ideas in the analysis of missing data are (a) the EM algorithm [Dempster, Laird and Rubin, J. Roy. Statist. Soc. Ser. B 39 (1977) 1--38] for maximum likelihood (ML) estimation, and (b) the formulation of models for the joint distribution of the data ${Z}$ and missing data indicators ${M}$, and associated "missing at random"; (MAR) condition under which a model for ${M}$ is unnecessary [Rubin, Biometrika 63 (1976) 581--592]. Most previous work has treated ${Z}$ and ${M}$ as single blocks, yielding selection or pattern-mixture models depending on how their joint distribution is factorized. This paper explores "block-sequential"; models that interleave subsets of the variables and their missing data indicators, and then make parameter restrictions based on assumptions in each block. These include models that are not MAR. We examine a subclass of block-sequential models we call block-conditional MAR (BCMAR) models, and an associated block-monotone reduced likelihood strategy that typically yields consistent estimates by selectively discarding some data. Alternatively, full ML estimation can often be achieved via the EM algorithm. We examine in some detail BCMAR models for the case of two multinomially distributed categorical variables, and a two block structure where the first block is categorical and the second block arises from a (possibly multivariate) exponential family distribution.Comment: Published in at http://dx.doi.org/10.1214/10-STS344 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Comprehending narrative: the cognitive dimension

Readers of narratives construct complex mental models or "spaces" within which to locate themselves. During this process, readers construct, activate, and adjust a spatio-temporal focus to integrate interpretation of individual sentences in a global interpretation. This focus, the ‘deictic center’, shifts constantly. Although linguistic markings help orient the readers, they must draw not only on complex inferential skill but also schematic socio-cultural knowledge. This can create difficulties for readers from other linguistic and cultural environments. Examples from several narratives and a poem are examined, and the cognitive skills required are considered. In each, a base reality “of this time, of that place’ is established, and readers are moved from that mental space to spaces representing other times and places, real and hypothetical, which may include counterparts of events and participants already encountered. The notion of ‘sameness’ is thus a complex one, since it links counterparts across different kinds of spaces. In our examples, each author uses sometimes subtle linguistic markers pointing to sociocultural schemata assumed familiar to the assumed readership. Readers from other social and cultural contexts must surmount the differences in order to construct a plausible cognitive model of the narrative

La nature, le rôle et l'influence de la doctrine universitaire en droit administratif québécois

In view of the increasingly divergent tendencies in legal scholarship, many authors are reconsidering whether « la doctrine » can really serve as a formal source of law. Since university professors are primarly responsible for producing this scholarly commentary, at least in the field of administrative law, it is worth asking two related questions : first, does university scholarship in law have a specific purpose or logic ? and second, does the nature of administrative law require that this scholarship have a particular direction ? In this essay, both questions are answered in the affirmative : University legal scholarship has a synthetic function not shared by ordinary legal writing, and given the case law foundations of the administrative law, this scholarship must also reveal the underlying conceptual structure of the subject

Accessibilité pour qui ? Selon quelles conceptions de la justice ?

Le rapport du Groupe de travail sur l’accessibilité à la justice du Québec, intitulé Jalons pour une plus grande accessibilité à la justice, a été présenté en septembre 1991. Ses diverses recommandations ont visé plusieurs matières : l'aide juridique, les programmes d'assurance frais juridiques, la Cour des petites créances, les modes non judiciaires de règlement de conflits, l'information et l'éducation juridique, et les besoins particuliers de certains groupes cibles tels que les communautés culturelles et les autochtones. Le présent essai a pour objet de situer les recommandations du Groupe de travail dans le contexte du débat actuel parmi les juristes québécois sur la « déjuridicisation », la déjudiciarisation et le droit préventif. Il soulève également la critique de notre système de justice évoquée par les tenants de la philosophie postmoderne. Le texte offre en conclusion quelques suggestions pour une reconceptualisation de l'accessibilité à la justice discutées au sein du Groupe de travail mais qui n'ont pas été traduites en recommandations formelles.The Report of the Quebec Task Force on Accessibility to Justice entitled Steps Toward a Greater Accessibility to Justice was submitted in September 1991. Its various recommendations treated subjects as disparate as legal aid, pre-paid legal insurance, the small claims court, alternative dispute resolution, legal information and education, and the special needs of non-mainstream groups such as cultural communities and aboriginal peoples. This essay situates the various recommendations of the Task Force within the larger debate about dejuridicization, dejudi-cialization and preventive law which is animating Quebec jurists today. It also raises certain challenges to our current conception of legal justice flowing from the post-modern critique of society. The essay concludes with a number of suggestions for broadening our conception of access to justice which were discussed by the Task Force but which were not the object of any formal recommendations

Regulatory influence in a Honolulu adult education program, 2003-2005: A case study

This study traces how regulatory compliance precipitated an adult education institution’s shift from open to managed enrollment. That shift was prompted by three administrative concerns derived from regulatory mandates: a requirement of data quality, a requirement of population coverage, and strong pressure for student promotion through the observed educational system. Richards and Lockhart (1996, p. 38) wrote: “Any language teaching program reflects both the culture of the institution... as well as collective decisions and beliefs of individual teachers.” Regulatory compliance produced a tension between principles and funding, and this paper examines the impact on institutional culture that resulted at one case

Entre l'efficience de Justinien et la justice de Locke

Aujourd'hui, il est courant de qualifier les rapports humains les plus importants comme étant les rapports économiques. Les économies nationales subissent toutes sortes de perturbations économiques (des perturbations naturelles, résultant de décisions politiques ou encore de nouvelles technologies. Nos gouvernements sont appelés à y répondre. Doivent-ils laisser ces changements s'effectuer d'eux-mêmes ou résister à ceux-ci ? Doivent-ils tenter de les freiner ou au contraire les faciliter ? Il est clair qu'il n'existe pas de réponse unique applicable dans toutes les circonstances. Chacune des situations particulières exigera la recherche d'un équilibre entre l'efficience économique et la justice sociale. Il ne faut pas présumer que la notion de justice dans le domaine juridique peut se réduire à la simple notion d'efficacité économique. Et il ne convient pas non plus de supposer que la notion de justice dans le domaine économique peut se limiter à la simple recherche de la richesse maximale.Today, the most important of our human relationships are typically cast as economic. National economies are subject to a number of different kinds of shocks (natural shocks, shocks resulting from political decisions, shocks resulting from technology. Governments are called upon to respond. Should they simply let the market take its course ? Should they intervene to slow down the pace of change ? Should they facilitate change ? Should they resist change at all cost ? One thing is certain : there is no response that is adequate to every situation. The appropriate response involves a careful balancing of efficiency concerns and concerns of social justice. We do ourselves a great disservice if we think that justice in the legal sphere can be reduced to the notion of efficient corrective justice. And we also do ourselves a great disservice if we think that justice in the economic sphere can be reduced to simple questions of wealth maximization

Quantitative magnetic resonance image analysis via the EM algorithm with stochastic variation

Quantitative Magnetic Resonance Imaging (qMRI) provides researchers insight into pathological and physiological alterations of living tissue, with the help of which researchers hope to predict (local) therapeutic efficacy early and determine optimal treatment schedule. However, the analysis of qMRI has been limited to ad-hoc heuristic methods. Our research provides a powerful statistical framework for image analysis and sheds light on future localized adaptive treatment regimes tailored to the individual's response. We assume in an imperfect world we only observe a blurred and noisy version of the underlying pathological/physiological changes via qMRI, due to measurement errors or unpredictable influences. We use a hidden Markov random field to model the spatial dependence in the data and develop a maximum likelihood approach via the Expectation--Maximization algorithm with stochastic variation. An important improvement over previous work is the assessment of variability in parameter estimation, which is the valid basis for statistical inference. More importantly, we focus on the expected changes rather than image segmentation. Our research has shown that the approach is powerful in both simulation studies and on a real dataset, while quite robust in the presence of some model assumption violations.Comment: Published in at http://dx.doi.org/10.1214/07-AOAS157 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org