240 research outputs found
Beyond first-order asymptotics for Cox regression
To go beyond standard first-order asymptotics for Cox regression, we develop
parametric bootstrap and second-order methods. In general, computation of
-values beyond first order requires more model specification than is
required for the likelihood function. It is problematic to specify a censoring
mechanism to be taken very seriously in detail, and it appears that
conditioning on censoring is not a viable alternative to that. We circumvent
this matter by employing a reference censoring model, matching the extent and
timing of observed censoring. Our primary proposal is a parametric bootstrap
method utilizing this reference censoring model to simulate inferential
repetitions of the experiment. It is shown that the most important part of
improvement on first-order methods - that pertaining to fitting nuisance
parameters - is insensitive to the assumed censoring model. This is supported
by numerical comparisons of our proposal to parametric bootstrap methods based
on usual random censoring models, which are far more unattractive to implement.
As an alternative to our primary proposal, we provide a second-order method
requiring less computing effort while providing more insight into the nature of
improvement on first-order methods. However, the parametric bootstrap method is
more transparent, and hence is our primary proposal. Indications are that
first-order partial likelihood methods are usually adequate in practice, so we
are not advocating routine use of the proposed methods. It is however useful to
see how best to check on first-order approximations, or improve on them, when
this is expressly desired.Comment: Published at http://dx.doi.org/10.3150/13-BEJ572 in the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Modified Profile Likelihood for Fixed-Effects Panel Data Models
We show how modified profile likelihood methods, developed in the statistical literature, may be effectively applied to estimate the structural parameters of econometric models for panel data, with a remarkable reduction of bias with respect to ordinary likelihood methods. Initially, the implementation of these methods is illustrated for general models for panel data including individual-specific fixed effects and then, in more detail, for the truncated linear regression model and dynamic regression models for binary data formulated along with different specifications. Simulation studies show the good behavior of the inference based on the modified profile likelihood, even when compared to an ideal, although infeasible, procedure (in which the fixed effects are known) and also to alternative estimators existing in the econometric literature. The proposed estimation methods are implemented in an R package that we make available to the reader
Opportunities and barriers for adoption of a decision-support tool for Alzheimer's Disease
Clinical decision-support tools (DSTs) represent a valuable resource in healthcare. However, lack of Human
Factors considerations and early design research has often limited their successful adoption. To complement
previous technically focused work, we studied adoption opportunities of a future DST built on a predictive
model of Alzheimer’s Disease (AD) progression. Our aim is two-fold: exploring adoption opportunities for
DSTs in AD clinical care, and testing a novel combination of methods to support this process. We focused
on understanding current clinical needs and practices, and the potential for such a tool to be integrated
into the setting, prior to its development. Our user-centred approach was based on field observations and
semi-structured interviews, analysed through workflow analysis, user profiles, and a design-reality gap model.
The first two are common practice, whilst the latter provided added value in highlighting specific adoption
needs. We identified the likely early adopters of the tool as being both psychiatrists and neurologists based in
research-oriented clinical settings. We defined ten key requirements for the translation and adoption of DSTs
for AD around IT, user, and contextual factors. Future works can use and build on these requirements to stand
a greater chance to get adopted in the clinical setting
Requirements for a Dashboard to Support Quality Improvement Teams in Pain Management
Pain management is often considered lower priority than many other aspects of health management in hospitals. However, there is potential for Quality Improvement (QI) teams to improve pain management by visualising and exploring pain data sets. Although dashboards are already used by QI teams in hospitals, there is limited evidence of teams accessing visualisations to support their decision making. This study aims to identify the needs of the QI team in a UK Critical Care Unit (CCU) and develop dashboards that visualise longitudinal data on the efficacy of patient pain management to assist the team in making informed decisions to improve pain management within the CCU. This research is based on an analysis of transcripts of interviews with healthcare professionals with a variety of roles in the CCU and their evaluation of probes. We identified two key uses of pain data: direct patient care (focusing on individual patient data) and QI (aggregating data across the CCU and over time); in this paper, we focus on the QI role. We have identified how CCU staff currently interpret information and determine what supplementary information can better inform their decision making and support sensemaking. From these, a set of data visualisations has been proposed, for integration with the hospital electronic health record. These visualisations are being iteratively refined in collaboration with CCU staff and technical staff responsible for maintaining the electronic health record. The paper presents user requirements for QI in pain management and a set of visualisations, including the design rationale behind the various methods proposed for visualising and exploring pain data using dashboards
INHIBITORY EFFECT OF BIOCIDES ON ENVIRONMENTAL S. AUREUS STRAINS
The aim of this study was to evaluate the inhibitory effect of biocides on S.aureus strains isolated in dairy environment. After a contact time of 5' all tested molecules showed total growth inhibition of bacteria; for lower contact time results were depending on strains and biocides
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