1,721,007 research outputs found
Penalized likelihood inference in meta-regression
No full textRandom-effects models are frequently used to synthesise information from different studies in meta-analysis. While likelihood-based inference is attractive both in terms of limiting properties and in terms of implementation, its application in random-effects meta-analysis may result in misleading conclusions, especially when the number of studies is small to moderate. The current paper shows how methodology that reduces the asymptotic bias of the maximum likelihood estimator of the variance component can also substantially improve inference about the mean effect size. The results are derived for the more general framework of random-effects meta-regression, which allows the mean effect size to vary with study-specific covariates
Distributional Fairness in Road Safety Policies: Α Discrete Choice Approach to Explore Citizens’ Preferences on the Distribution of the Effects of Road Safety Policies
No full textThis study aims to explore the preferences of citizens regarding fairness considerations related to the distribution of the effects of road safety policies in order to provide with policy recommendations that will help to promote more fair road safety policies. To achieve this aim the Discrete Choice Approach is going to be followed, using stated preference data. This requires a Stated Preference experiment to be conducted, which consists of two distinct parts. The first part is related to the citizen’s perception of fairness of different types of distribution of the effects of road safety policies, while the second one is related with the importance of this perceived fairness in the preference of citizens over specific road safety policy alternatives. In the first case, two Linear Regression models have been estimated, while for the second case, three Discrete Choice models. This study has shown that the Discrete Choice Approach can actually give some insight to moral dilemmas as it is suggested in literature. It also showed that low public acceptance can be a show-stopper for road safety policies, thus looking only at the aggregate effects of a road safety policy can be often misleading. The way that the effects of road safety policies are distributed among different groups of people can have a significant influence on the public acceptance of road safety policies.Civil Engineering | Transport and Plannin
Advances in statistical methods for large-scale binary-valued neuroimaging data
Full text linkWhite matter lesions are common in the ageing brain and their size, location, and
evolution have been shown to be informative of diagnosis, treatment, or prevention of
neurological conditions such as multiple sclerosis. The work presented in this thesis explores the use of voxel-based approaches for modelling binary lesion data obtained from
brain Magnetic Resonance Imaging scans. We seek to develop methods that are computationally efficient and stable for massive datasets with very low lesion incidence, and
demonstrate the value of these methods with a real dataset to disentangle contributing
risk factors of lesion incidence.
Our contributions are spread across three main chapters including two published
articles and one preprint, and they could be summarised as
Chapter 2 Kindalova et al. (2021a) explore whether the potential gains in estimator accuracy justify the use of a more computationally intensive spatial
modelling approach as opposed to a mass-univariate approach to modelling voxel-wise binary lesion data. A method comparison of three crosssectional lesion mapping approaches is facilitated through the development of a novel simulation framework of artificial lesion masks, which
mimics features of real lesion masks.
Chapter 3 Veldsman et al. (2020) use data on 13,680 healthy ageing UK Biobank
participants at one time point to explore the effects of the individual
cerebrovascular risk factors (e.g. waist-to-hip ratio and smoking) on lesion
load and on lesion probability, which has been an obstacle in the literature
so far due to the dominating effect of hypertension and the presence of
comorbidities.
Chapter 4 Kindalova et al. (2021b) adopt a generalized estimating equations approach to modelling longitudinal binary-valued outcomes. By adding a
Jeffreys-prior penalty to log-link generalized estimating equations for relative risk regression, finiteness of the estimates along with superior convergence rate are demonstrated in an extensive simulation study as well
as in a UK Biobank application on 1,578 participants with data from 2
visits
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Accessibility of bus transport in Nord-Jæren
Full text linkIn line with aims of making the transport sector more sustainable, accessible bus service is
essential. Nord-Jæren is an exciting geographical area concerning this because of heavy
investments made here on bus rapid transit (BRT) infrastructure in recent and coming years.
This thesis examines how accessible bus transport is in urban Nord-Jæren before the completion
of this BRT project, named the Bus Road (“Bussveien”). Additionally, it assesses whether areas
with higher address densities have better bus accessibility and vice versa.
Bus accessibility throughout urban Nord-Jæren is found from a system perspective by
measuring six factors identified to influence bus transport accessibility. These are access
distance, service coverage, travel time, bus route options, frequency, and service span. Each
factor affects spatial or temporal and local or network accessibility. This thesis contains
measures of how well each basic statistical unit (“grunnkrets”) and statistical tract
(“delområde”) in the research area perform in the abovementioned accessibility factors,
categories, and overall.
The results indicate that bus transport is generally most accessible in and between Stavanger
and Sandnes city centres, where the first part of the Bus Road will come. In addition, some
areas west and north of Stavanger city centre are also among the most accessible by bus
transport. South and east of Sandnes city centre, less accessible areas exist, while Randaberg
and Sola municipalities have the least accessible areas. Generally, the least accessible areas
have among the lowest address densities, notably less than 500 addresses/km2. However,
many low-density areas are also among the most accessible.
The findings in this thesis may be used to identify areas in Nord-Jæren with poor bus
transport accessibility. In addition, they can explain why some areas have poorer accessibility
than others and how it can be improved
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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