Continuous Margin Research Articles

Computationally efficient Bayesian estimation of high-dimensional Archimedean copulas with discrete and mixed margins

Estimating copulas with discrete marginal distributions is challenging, especially in high dimensions, because computing the likelihood contribution of each observation requires evaluating $$2^{J}$$ terms, with J the number of discrete variables. Our article focuses on the estimation of Archimedean copulas, for example, Clayton and Gumbel copulas. Currently, data augmentation methods are used to carry out inference for discrete copulas and, in practice, the computation becomes infeasible when J is large. Our article proposes two new fast Bayesian approaches for estimating high-dimensional Archimedean copulas with discrete margins, or a combination of discrete and continuous margins. Both methods are based on recent advances in Bayesian methodology that work with an unbiased estimate of the likelihood rather than the likelihood itself, and our key observation is that we can estimate the likelihood of a discrete Archimedean copula unbiasedly with much less computation than evaluating the likelihood exactly or with current simulation methods that are based on augmenting the model with latent variables. The first approach builds on the pseudo-marginal method that allows Markov chain Monte Carlo simulation from the posterior distribution using only an unbiased estimate of the likelihood. The second approach is based on a variational Bayes approximation to the posterior and also uses an unbiased estimate of the likelihood. We show that the two new approaches enable us to carry out Bayesian inference for high values of J for the Archimedean copulas where the computation was previously too expensive. The methodology is illustrated through several real and simulated data examples.

Demineralized enamel reduces margin integrity of self-etch, but not of etch-and-rinse bonded composite restorations.

The aim of this study was to investigate margin integrity of Class V composite restorations in demineralized and sound enamel after bonding with different etch-and-rinse and self-etch adhesive systems. Out of a total of 60 specimens from bovine incisors, 30 specimens were demineralized (21days, acid buffer, pH 4.95) to create artificial enamel lesions. Circular Class V cavities were prepared in all 60 specimens and treated with either an unfilled etch-and-rinse adhesive (Syntac Classic; Ivoclar Vivadent), a filled etch-and-rinse adhesive (Optibond FL; Kerr), or a self-etch adhesive (iBond Self Etch; Heraeus) (n = 10 per group). The cavities were restored with a nanofilled resin composite and thermocycled (5000×, 5-55°C). Scanning electron microscopy was used to evaluate margin integrity of the composite restorations, and the percentage of continuous margin was statistically analyzed (α = 0.05). Demineralized enamel led to a significantly lower margin integrity when the self-etch adhesive iBond Self Etch was applied, but did not affect margin integrity when the etch-and-rinse adhesives Optibond FL (filled) or Syntac Classic (unfilled) were used. No significant differences in margin integrity in sound and demineralized enamel were observed between the different adhesives. Demineralized enamel reduces margin integrity of composite restorations when bonded with a self-etch adhesive, but does not affect margin integrity when an etch-and-rinse approach is used.

Efficient MCMC estimation of some elliptical copula regression models through scale mixtures of normals

AbstractThis paper proposes an efficient estimation method for some elliptical copula regression models by expressing both copula density and marginal density functions as scale mixtures of normals (SMN). Implementing these models using the SMN is novel and allows efficient estimation via Bayesian methods. An innovative algorithm for the case of complex semicontinuous margins is also presented. We utilize the facts that copulas are invariant to the location and scale of the margins; all elliptical distributions have the same correlation structure; and some densities can be represented by the SMN. Two simulation studies, one on continuous margins and the other on semicontinuous margins, highlight the favorable performance of the proposed methods. Two empirical studies, one on the US excess returns and one on the Thai wage earnings, further illustrate the applicability of the proposals.

The “left behind”: Smallholders in contemporary Russian agriculture

AbstractSmallholder production in Russia has been in decline for more than a decade. The likelihood is for continued marginalization. Smallholders confront four obstacles. First, path dependencies, which includes the fact that smallholders' production remains traditional and subsistence oriented. Second, institutions in the form of state policy restrict land and animals. Third, Russia's role in the third food regime means that smallholders are unable to help Russia's emergence as a global food superpower. Fourth, smallholders are being left behind in the ongoing technological revolution led by agroholdings. As technological advancement expands in scope, the gap between large farms and smallholders will widen.

Bayesian Inference for the One-Factor Copula Model

ABSTRACTWe develop efficient Bayesian inference for the one-factor copula model with two significant contributions over existing methodologies. First, our approach leads to straightforward inference on dependence parameters and the latent factor; only inference on the former is available under frequentist alternatives. Second, we develop a reversible jump Markov chain Monte Carlo algorithm that averages over models constructed from different bivariate copula building blocks. Our approach accommodates any combination of discrete and continuous margins. Through extensive simulations, we compare the computational and Monte Carlo efficiency of alternative proposed sampling schemes. The preferred algorithm provides reliable inference on parameters, the latent factor, and model space. The potential of the methodology is highlighted in an empirical study of 10 binary measures of socio-economic deprivation collected for 11,463 East Timorese households. The importance of conducting inference on the latent factor is motivated by constructing a poverty index using estimates of the factor. Compared to a linear Gaussian factor model, our model average improves out-of-sample fit. The relationships between the poverty index and observed variables uncovered by our approach are diverse and allow for a richer and more precise understanding of the dependence between overall deprivation and individual measures of well-being.

Mixed Marginal Copula Modeling

ABSTRACTThis article extends the literature on copulas with discrete or continuous marginals to the case where some of the marginals are a mixture of discrete and continuous components. We do so by carefully defining the likelihood as the density of the observations with respect to a mixed measure. The treatment is quite general, although we focus on mixtures of Gaussian and Archimedean copulas. The inference is Bayesian with the estimation carried out by Markov chain Monte Carlo. We illustrate the methodology and algorithms by applying them to estimate a multivariate income dynamics model. Supplementary materials for this article are available online.

Application of Calcium Silicate Materials After Acid Etching May Preserve Resin-Dentin Bonds.

The aim of the present study was to evaluate the effect of the application of calcium silicate materials (CSMs), after acid etching, on the longevity of the hybrid layer and marginal adaptation of composite restorations. Eighty human permanent molars received an intrapulpal pressure of 15 cm H2O. Sixty teeth received a mesial proximal slot preparation with the gingival margin extending 1 mm below the cemento-enamel junction. The samples were divided into two groups. Group 1 received restorations using two types of etch-and-rinse adhesives: ethanol based (Single Bond, 3M ESPE, St Paul, MN, USA) and acetone based (Prime & Bond NT, Dentsply, DeTrey GmbH, Germany). In group 2 samples, a commercially available CSM (ProRoot MTA) was allowed to set before grinding and placing into a distilled water solution. This solution was applied on the cavity floor after acid etching. The surface was washed after 30 seconds followed by application of adhesives and restorations as in group 1. The samples were stored in phosphate-buffered saline for six months, maintaining the intrapulpal pressure. An epoxy replica was made, and the marginal adaptation was evaluated using scanning electron microscopy. The percentage of continuous margin (CM) was recorded for each group. Another 20 samples were used for hybrid layer evaluation. The crowns were ground to expose dentin. Intrapulpal pressure was applied. The samples were divided into two groups and restored similar to samples restored for marginal adaptation evaluation. The samples were longitudinally cut in 1-mm slices. The slices were stored under 15 cm of phosphate-buffered saline to simulate the pulpal pressure. After six months, the adhesive interface was evaluated using a scanning electron microscope. Statistical analysis was done with two-way analysis of variance with Holm-Sidak's correction for multiple comparisons. Application of CSMs improved the marginal adaptation values in both adhesive groups. In group 1, there were areas of incomplete penetration of resins along with evidence of partial degradation of resin tags. Samples receiving CSM application after acid etching demonstrated long and regular resin tags with very few signs of degradation. Application of CSMs after acid etching can be a potential avenue in preserving the resin-dentin bonds.

Marginal quality of ceramic inlays after three different instrumental cavity preparation methods of the proximal boxes

ObjectivesThe marginal quality of ceramic inlays was evaluated after the use of three different instrumental finishing methods in mesio-occluso-distal (mod) cavity boxes in vitro after hydrothermal loading (HTL).Materials and methodsCaries-free human molars were divided into three groups. Mod-cavities were conventionally prepared. Box finishing was performed in every group with rotating (RI), sonic (SI), or ultrasonic (USI) instruments. Surface roughness was examined. Twelve mod-cavities remained untreated. Continuous margin quality was evaluated with scanning electron microscopy (SEM). Ceramic inlays were cemented into cavities. After HTL microleakage, marginal and absolute marginal gaps were examined. All data were analyzed statistically.ResultsSignificant differences were found, between cavity surface roughness of RI and SI groups, the RI and USI groups, but not between microleakage, marginal, absolute marginal gaps after HTL and in proximal marginal quality. No correlations between microleakage and marginal gaps nor between microleakage and surface roughness were found.ConclusionMod-cavity proximal box finishing with SI or USI resulted in a higher surface roughness than the use of RI. The type of the finishing method did not influence the marginal quality of ceramic inlays. For the mod-cavity finishing, the use of SI and USI could be an alternative instrumental method to conventional RI methods with a lower risk of iatrogenic damage of the adjacent teeth.Clinical relevanceThis study allows the practitioner to better determine the proper indications and limitations of the sonic and ultrasonic instruments for mod-cavity proximal box finishing.

The Language of Cataloguing: Deconstructing and Decolonizing Systems of Organization in Libraries

This paper analyzes the language of cataloguing because the information that librarians and other information professionals provide to others has a huge impact both on how others are viewed and how others view themselves. This ultimately comes down to the way in which words are given meaning and interpreted according to the socio-political climate of the time. As society, politics, and economies change, so too does the language of representation. Therefore, the Library of Congress subject headings (LCSH) as a system of categorization is only as effective as the language that is used to define what is and what is not. Moreover, those who control the language of categorization control access to the information categorized within that system. Consequently, librarians must always be critical of the language they are using in their information organization systems. Language is continuously evolving according to societal discourse and politics; therefore, if libraries are to maintain their social responsibility to provide information to all, including socially disadvantaged and marginalized peoples, then librarians must continuously advocate for changes to subject headings. Librarians must also recognize and reflect on their own internal biases when cataloguing and make it their job to deconstruct language and decolonize the systems that perpetuate the continued marginalization of others. To remain neutral about these systems is the very opposite of what it means to be a librarian in the twenty-first century.

Abstract P2-12-04: Surgeon performed intraoperative ultrasound accurately predicts margin status after neaoadjuvant chemotheraphy

Abstract Objective: Neoadjuvant chemotraphy (NACT) is the preferred option of treatment in locally advanced and select cases of early stage breast cancer, currently. One of the major aims is to downstage tumor status allowing more conservative surgery with the most acceptable cosmetic outcome. The presence or absence of residual invasive cancer after NACT, is one of the strong prognostic factors for risk of recurrence and the margin status is the other. Due to the excess degree of fibrosis after tumor shrinkage, to accurately predict margin status intraoperatively after NACT is a challenge for surgeon. The aim of the presented study is to evaluate the efficacy of continuous intraoperative ultrasound guided breast conserving surgery (IUG-BCS) in terms of margin status and re-excision rate. The relationship between intraoperative assessment of gross macroscopic and ultrasonographic margins and cavity shavings results, were also analyzed. Methods: Between 2014 and 2017, IUG-BCS were performed to 194 patients after NACT. Surgeon performed continuous peroperative real-time sonographic margin assessment during resection, macroscopic evaluation, specimen US including sonographic analysis of six faces of each specimen, and shaved cavity margins for permanent pathologic assessment were the standard steps of our methodology. Results: Of the 194 patients, 82 (42.5%) had pathologic complete response (pCR) after NAC. The sensitivity of intraoperative ultrasound localization was 100% (194/194 cases). Patients were on average 53 years old (range, 28-65). There was no difference with respect to patient characteristics including age, menopausal status, personal-family history, oral contraceptive usage, body mass index and tumor localization. Mean tumor size was 5.42 cm before NAC and 2.56 cm after NAC, for those excluding ypT0. Of the 112 patients without pCR, tumor free margins were obtained by means of IUG-BCS in 99% (665/672) of margins evaluated sonographically. Moreover, the involved margins were correctly identified by the surgeon via specimen sonography in %71.4 of the cases (5/7) which was confirmed by cavity shaving results. No frozen section analysis was performed and macroscopic evaluation of the specimen predicted nothing significant. According to permanent section analysis of the resected specimens and cavity shavings, no further intervention was required due to margin positivity. IUG-BCS with real-time specimen sonography were unable to predict involved margins in only two cases, both of them proved to be invasive lobular carcinoma without evidence of residual cancer on pathological examination of cavity shavings. Accordingly, negative margins were achieved in 100% of cases at the initial procedure verified by permanent analysis. Conclusion: Continuous intraoperative ultrasound with specimen sonography is an invaluable and effective modality to achieve negative surgical margins after NACT. Furthermore, meticulous sonographic assessment of specimen margins together with cavity shavings from tumor bed could be a feasible method to decrease re-excision rates without frozen section analysis leading to cost-effectiveness. However, the accuracy of sonography should be questioned in case of lobular histology. Citation Format: Karadeniz Cakmak G, Mutlu S, Sen H, Engin H, Bahadir B, Bakkal H. Surgeon performed intraoperative ultrasound accurately predicts margin status after neaoadjuvant chemotheraphy [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-12-04.

Performance of Monolithic and Veneered Zirconia Crowns After Endodontic Treatment and Different Repair Strategies

To investigate failure loads of monolithic and veneered all-ceramic crowns after root canal treatment and to analyze marginal integrity of repair fillings. Seventy-two human molars were restored with monolithic (Zr-All) or veneered (Zr-Ven) zirconia crowns. Molars were assigned to six groups (n=12 per group) depending on restoration material, access type (no access cavity [control] or endodontic treatment [test]), and type of filling (one-step [1-st] or two-step [2-st]). For type of filling, molars were treated using a self-etch universal adhesive and cavities were either filled with layered composite (1-st) or filled until the crown material was reached, which was additionally conditioned and then filled (2-st). Scanning electron microscopic analysis of the restoration margins was performed before and after thermomechanical loading (TML), and the percentage of continuous margins was assessed. Crowns were then loaded to failure. Preparation of the access cavity required more time in monolithic (445 s) than in veneered crowns (342 s). Loads to failure were higher in control groups (Zr-All: 5814 N; Zr-Ven: 2133 N) and higher in monolithic test (2985 N) than in veneered test crowns (889 N). In monolithic crowns, 1-st had lower fracture loads than 2-st fillings (2149 N vs 3821 N). Continuous margins of 66% to 71% were achieved, which deteriorated after TML by 39% to 40% in Zr-All, by 34% in Zr-Ven-1-st, and by 24% in Zr-Ven-2-st. Endodontic access and adhesive restorations resulted in reduced fracture load in monolithic and veneered zirconia crowns. Two-step fillings provided higher fracture loads in Zr-All and better marginal quality in Zr-Ven crowns.

Citizenship and Community Mental Health Care.

Citizenship is an approach to supporting the social inclusion and participation in society of people with mental illnesses. It is receiving greater attention in community mental health discourse and literature in parallel with increased awareness of social determinants of health and concern over the continued marginalization of persons with mental illness in the United States. In this article, we review the definition and principles of our citizenship framework with attention to social participation and access to resources as well as rights and responsibilities that society confers on its members. We then discuss our citizenship research at both individual and social-environmental levels, including previous, current, and planned efforts. We also discuss the role of community psychology and psychologists in advancing citizenship and other themes relevant to a citizenship perspective on mental health care and persons with mental illness.

Applying Indigenizing Principles of Decolonizing Methodologies in University Classrooms

This case study examines ongoing work to Indigenize education programs at one Canadian university. The history of the academy in Canada has been dominated by Western epistemologies, which have devalued Indigenous ways of knowing and set the grounds for continued marginalization of Indigenous students, communities, cultures, and histories. We argue that institutions of higher learning need to move away from the myopic lens used to view education and implement Indigenizing strategies in order to counteract the systemic monopolization of knowledge and communication. Faculties of education are taking a leading role in Canadian universities by hiring Indigenous scholars and incorporating Indigenous ways of knowing into teacher education courses. Inspired by the 25 Indigenous principles outlined by Maōri scholar Linda Tuhiwai Smith (2012), four Indigenous faculty members from Western Canada document effective decolonizing practices for classroom experience, interaction, and learning that reflect Indigenous values and orientations within their teaching practices.

Applying Indigenizing Principles of Decolonizing Methodologies in University Classrooms

This case study examines ongoing work to Indigenize education programs at one Canadian university. The history of the academy in Canada has been dominated by Western epistemologies, which have devalued Indigenous ways of knowing and set the grounds for continued marginalization of Indigenous students, communities, cultures, and histories. We argue that institutions of higher learning need to move away from the myopic lens used to view education and implement Indigenizing strategies in order to counteract the systemic monopolization of knowledge and communication. Faculties of education are taking a leading role in Canadian universities by hiring Indigenous scholars and incorporating Indigenous ways of knowing into teacher education courses. Inspired by the 25 Indigenous principles outlined by Maōri scholar Linda Tuhiwai Smith (2012), four Indigenous faculty members from Western Canada document effective decolonizing practices for classroom experience, interaction, and learning that reflect Indigenous values and orientations within their teaching practices.

Intersecting race, space, and place through community gardens

AbstractIn this article, we examine the structure and meaning of community gardens in Florida's most cohesive and oldest African American community of Frenchtown in Tallahassee. Here, residents reclaim and transform empty spaces into places of engagement and empowerment, effectively resisting systemic racism. Using a mixed methods approach during a 5‐week NSF‐funded ethnographic field school with the Health Equity Alliance of Tallahassee, we counter the prevailing stigma of Frenchtown that perpetuates its continued marginalization. We argue that community gardens are expressions of social resistance. Through garden activities, residents transcend race, culture, income, and neighborhoods, while also promoting health, heritage, place‐making, and economic opportunities. Place is constituted by spatial politics in a cultural milieu, evident in the community's ability to intersect diverse institutional boundaries via gardens. This research contextualizes how a community‐based participatory research project successfully resists violent environments through spatial transformation.

Social Constructions of Childhood: From Not-Yet-Adults to People in Their Own Right

Across the globe it is clear that children are a marginalized group. Children are not allowed to vote or be taken seriously in political circles (Sharpe, 2015), are kept away from public spaces (Valentine 2004), navigate inhospitable working conditions (Gamlin et. al., 2015), and are rapidly losing the time and space to foster their own child culture (Woolley and Griffin, 2014). Adults continue to institutionalize children’s play and restrict children’s access to public space. This serves to reinforce children’s position as second-class citizens. A mounting body of work shows that children are suffering in their physical and social development due to this continued marginalization (Clements, 2004; Corsaro, 1997; Evaldsson, 1998; Goodwin, 1990; Staempfli, 2008). This naturalized and troubling dynamic between children and adults needs to be critically examined in order to foster a healthy, socially just society.

“Everybody Loves a Redemption Story around Election Time”: Rob Ford and Media Construction of Substance Misuse and Recovery

The crack cocaine scandal that embroiled former Toronto Mayor Rob Ford presents an opportunity to explore how we think and talk about substance (mis)use and recovery. Examining 1,836 articles from four Canadian newspapers, we analyze the ways news media frame Ford's use of crack cocaine. We find that Ford's drug use was often linked to a police investigation into gangs and guns, and much was made of his association with “Somali” drug dealers. Not only does this framing perpetuate prevailing stereotypes (crack cocaine use by racialized individuals living in poor and violent communities), but also it encourages the public to consider drugs a criminal justice issue and contributes to the stigma associated with drug use. Moreover, news media repeatedly suggested that Ford's problematic drug use could be solved if he took a leave from his job and entered a treatment facility. However, Ford's refusal to express shame and seek immediate treatment made him unworthy of compassion and instead rendered him deserving of censure. We argue that news media promoting a narrow pathway to addiction recovery and redemption ignores the realities of problematic drug use and justifies the continued marginalization of those who fail to meet this strict code of conduct.

Being Left Behind Amidst Africa’s Rising Imagery: The Maasai In The World Of Information And Communication Technologies (ICTs)

Today the media is replete with stories about Africa rising and enjoying middle –income status. Those promoting the narrative of Africa rising include the World Bank and western –trained elites. The narrative of success assumes that prosperity trickles down to Indigenous communities, who are pictured consuming mobile phones and tablets. At the same time, Hollywood and western media outlets continue to present images of Indigenous Maasai as a cultural export to be consumed. With emphasis on social media narratives, this paper interrogates the continued marginalisation of the Maasai people amidst the myth of a rising Africa. In sum, the Africa rising myth and penetration of ICTs in rural areas masks the dispossession of Maasai means of livelihood, and therefore worsening the groups’ conditions of living.

High-grade calcareous metasediments from the Sawtooth Metamorphic Complex, Idaho, USA: evidence for passive margin strata and polymetamorphism within the Idaho batholith

ABSTRACTThe Sawtooth Metamorphic Complex (SMC) of central Idaho contains exposures of metasupracrustal rocks, in a crucial location between the Archaean Wyoming craton to the east and the adjacent Mesozoic terranes to the west, that provide constraints on Precambrian crustal evolution in the northwestern United States. Mineral textures, whole-rock geochemistry, and thermobarometry of calc-silicate gneisses record multiple stages of crustal evolution, including protolith deposition, burial and multiple metamorphic and deformational overprints. Whole-rock signatures are consistent with derivation from post-Archaean, continental sources that have undergone sedimentary maturation and recycling typical of clastic sedimentation in passive-margin environments and with a metamorphosed sequence of calcareous sandstones and marls, containing varying proportions of clay and quartzo-feldspathic detritus. The sandstone-to-marl continuum may reflect a shallow-to-deep water transition in the depositional environment of the calc-silicate protoliths. Two metamorphic events and three deformational events are preserved. The assemblage clinopyroxene + quartz + plagioclase + K-feldspar + rutile represents peak metamorphic conditions (M1), estimated at 750–775°C with relatively oxidized metamorphic fluids, during development of D1a foliation. Deformation twinning in clinopyroxene records a widespread, high strain D1b event at high temperature. A second static thermal event (M2), associated with randomly oriented amphiboles overprinting M1 and D1b features, records conditions of ~550–725°C and H2O-rich fluids. Late-stage, brittle–ductile D2 deformation is characterized by mylonitic lenses of quartz, fractures within M1 clinopyroxenes that crosscut D1b deformation twins, and localized fracturing of M2 amphiboles. Geochemical and mineral chemical signatures of SMC calc-silicates preserve fingerprints of the original protolith through burial to mid-crustal conditions and high-grade metamorphism and suggest crustal thickening to about 20 km. The SMC may reflect rocks at depth beneath the Idaho batholith. These data, indicative of newly recognized post-Archaean terrain with passive-margin, continental sediments suggest that a continuous Cordilleran passive margin sequence may have extended along the western edge of Laurentia.

Bivariate copula additive models for location, scale and shape

In generalized additive models for location, scale and shape (GAMLSS), the response distribution is not restricted to belong to the exponential family and all the model’s parameters can be made dependent on additive predictors that allow for several types of covariate effects (such as linear, non-linear, random and spatial effects). In many empirical situations, however, modeling simultaneously two or more responses conditional on some covariates can be of considerable relevance. The scope of GAMLSS is extended by introducing bivariate copula models with continuous margins for the GAMLSS class. The proposed computational tool permits the copula dependence and marginal distribution parameters to be estimated simultaneously, and each parameter to be modeled using an additive predictor. Simultaneous parameter estimation is achieved within a penalized likelihood framework using a trust region algorithm with integrated automatic multiple smoothing parameter selection. The introduced approach allows for straightforward inclusion of potentially any parametric marginal distribution and copula function. The models can be easily used via the copulaReg() function in the R package SemiParBIVProbit. The proposal is illustrated through two case studies and simulated data.