Modeling Caries Experience: Advantages of the Use of the Hurdle Model

2016 ◽  
Vol 50 (6) ◽  
pp. 517-526 ◽  
Author(s):  
Hedwig Hofstetter ◽  
Elise Dusseldorp ◽  
Achim Zeileis ◽  
Annemarie A. Schuller
Keyword(s):  
Linear Models ◽  
Skewed Distribution ◽  
Caries Experience ◽  
Hurdle Model ◽  
Special Focus ◽  
Online Supplementary Material ◽  
Dmf Index ◽  
Supplementary Material ◽  
Hurdle Regression ◽  
Zero Counts

In dental epidemiology, the decayed (D), missing (M), and filled (F) teeth or surfaces index (DFM index) is a frequently used measure. The DMF index is characterized by a strongly positive skewed distribution with a large stack of zero counts for those individuals without caries experience. Therefore, standard generalized linear models often lead to a poor fit. The hurdle regression model is a highly suitable class to model a DMF index, but its use is subordinated. We aim to overcome the gap between the suitability of the hurdle model to fit DMF indices and the frequency of its use in caries research. A theoretical introduction to the hurdle model is provided, and an extensive comparison with the zero-inflated model is given. Using an illustrative data example, both types of models are compared, with a special focus on interpretation of their parameters. Accompanying R code and example data are provided as online supplementary material.

scholarly journals Stochastic daily precipitation model with a heavy-tailed component

2014 ◽  
Vol 14 (9) ◽  
pp. 2321-2335 ◽  
Author(s):  
N. M. Neykov ◽  
P. N. Neytchev ◽  
W. Zucchini
Keyword(s):  
Linear Models ◽  
Daily Precipitation ◽  
Daily Rainfall ◽  
Binary Logistic Regression ◽  
Skewed Distribution ◽  
Generalized Pareto ◽  
Precipitation Model ◽  
Standard Models ◽  
Heavy Tailed ◽  
Standard Software

Abstract. Stochastic daily precipitation models are commonly used to generate scenarios of climate variability or change on a daily timescale. The standard models consist of two components describing the occurrence and intensity series, respectively. Binary logistic regression is used to fit the occurrence data, and the intensity series is modeled using a continuous-valued right-skewed distribution, such as gamma, Weibull or lognormal. The precipitation series is then modeled using the joint density, and standard software for generalized linear models can be used to perform the computations. A drawback of these precipitation models is that they do not produce a sufficiently heavy upper tail for the distribution of daily precipitation amounts; they tend to underestimate the frequency of large storms. In this study, we adapted the approach of Furrer and Katz (2008) based on hybrid distributions in order to correct for this shortcoming. In particular, we applied hybrid gamma–generalized Pareto (GP) and hybrid Weibull–GP distributions to develop a stochastic precipitation model for daily rainfall at Ihtiman in western Bulgaria. We report the results of simulations designed to compare the models based on the hybrid distributions and those based on the standard distributions. Some potential difficulties are outlined.

scholarly journals Generalized Born radii computation using linear models and neural networks

2019 ◽  
Vol 36 (6) ◽  
pp. 1757-1764
Author(s):  
Saida Saad Mohamed Mahmoud ◽  
Gennaro Esposito ◽  
Giuseppe Serra ◽  
Federico Fogolari
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Linear Model ◽  
Correlation Coefficient ◽  
Linear Models ◽  
Reference Method ◽  
Supplementary Information ◽  
Model Parameters ◽  
Generalized Born ◽  
Supplementary Material

Abstract Motivation Implicit solvent models play an important role in describing the thermodynamics and the dynamics of biomolecular systems. Key to an efficient use of these models is the computation of generalized Born (GB) radii, which is accomplished by algorithms based on the electrostatics of inhomogeneous dielectric media. The speed and accuracy of such computations are still an issue especially for their intensive use in classical molecular dynamics. Here, we propose an alternative approach that encodes the physics of the phenomena and the chemical structure of the molecules in model parameters which are learned from examples. Results GB radii have been computed using (i) a linear model and (ii) a neural network. The input is the element, the histogram of counts of neighbouring atoms, divided by atom element, within 16 Å. Linear models are ca. 8 times faster than the most widely used reference method and the accuracy is higher with correlation coefficient with the inverse of ‘perfect’ GB radii of 0.94 versus 0.80 of the reference method. Neural networks further improve the accuracy of the predictions with correlation coefficient with ‘perfect’ GB radii of 0.97 and ca. 20% smaller root mean square error. Availability and implementation We provide a C program implementing the computation using the linear model, including the coefficients appropriate for the set of Bondi radii, as Supplementary Material. We also provide a Python implementation of the neural network model with parameter and example files in the Supplementary Material as well. Supplementary information Supplementary data are available at Bioinformatics online.

Cement plug technique for the management of disc-associated cervical spondylopathy in 52 Dobermann Pinscher dogs

2016 ◽  
Vol 29 (03) ◽  
pp. 195-201 ◽  
Author(s):  
Jonathan Pink ◽  
Toby Gemmill ◽  
Malcolm McKee
Keyword(s):  
Bone Cement ◽  
Vertebral Body ◽  
Cervical Disc ◽  
Adjacent Segment ◽  
Variable Degree ◽  
Cervical Spondylopathy ◽  
Online Supplementary Material ◽  
Supplementary Material ◽  
Neurologically Normal ◽  
Cement Plug

SummaryObjectives: To report the radiographic and clinical outcome of an intervertebral bone cement plug technique for the management of disc-associated cervical spondylopathy in Dobermann Pinscher dogs.Methods: Retrospective study of 52 Dobermann Pinscher dogs.Results: A variable degree of cement plug subsidence with loss of vertebral distraction was evident in all dogs (n = 40) that were radiographed >6 weeks postoperatively. In no case was there definitive evidence of vertebral body fusion. Eight dogs had a sudden deterioration in neurological status, cervical hyperaesthesia, or both between three days and 12 weeks following surgery that was considered to be implant-associated; six of these dogs were euthanatized. Following surgery, 43/52 dogs were considered to be neurologically normal or to have improved, however, nine of 43 subsequently deteriorated due to adjacent segment disease. At the long-term follow-up, 34 dogs were considered to be neurologically normal or to have improved. Twenty-nine dogs were dead by the end of the study period.Clinical significance: Intervertebral bone cement plug surgery results in an initial improvement in clinical signs in the majority of Dobermann Pinschers with disc-associated cervical spondylopathy. However, it fails to maintain vertebral distraction or achieve vertebral body fusion, and is associated with acute implant complications, additional cervical disc protrusions or mortality in a significant proportion of cases.Online Supplementary Material: Please note that online supplementary material for this paper is available at: http://dx.doi.org/10.3415/VCOT-15-09-0160.

scholarly journals Spatial Hurdle Models for Predicting the Number of Children with Lead Poisoning

2018 ◽  
Vol 15 (9) ◽  
pp. 1792 ◽  
Author(s):  
Zhen Zhen ◽  
Liyang Shao ◽  
Lianjun Zhang
Keyword(s):  
Lead Poisoning ◽  
Spatial Data ◽  
Linear Models ◽  
Negative Binomial ◽  
Lead Concentration ◽  
Hurdle Model ◽  
Soil Lead ◽  
Hurdle Models ◽  
Number Of Children ◽  
Block Level

Objective The purpose of this study is to identify the high-risk areas of children’s lead poisoning in Syracuse, NY, USA, using spatial modeling techniques. The relationships between the number of children’s lead poisoning cases and three socio-economic and environmental factors (i.e., building year and town taxable value of houses, and soil lead concentration) were investigated. Methods Spatial generalized linear models (including Poisson, negative binomial, Poisson Hurdle, and negative binomial Hurdle models) were used to model the number of children’s lead poisoning cases using the three predictor variables at the census block level in the inner city of Syracuse. Results The building year and town taxable value were strongly and positively associated with the elevated risk for lead poisoning, while soil lead concentration showed a weak relationship with lead poisoning. The negative binomial Hurdle model with spatial random effects was the appropriate model for the disease count data across the city neighborhood. Conclusions The spatial negative binomial Hurdle model best fitted the number of children with lead poisoning and provided better predictions over other models. It could be used to deal with complex spatial data of children with lead poisoning, and may be generalized to other cities.

Selected Restoration and Tooth Conditions: United States, 1988–1991

1996 ◽  
Vol 75 (2_suppl) ◽  
pp. 661-671 ◽  
Author(s):  
B.A. White ◽  
T.F. Albertini ◽  
L.J. Brown ◽  
D. Larach-Robinson ◽  
M. Redford ◽  
...  
Keyword(s):  
Dental Caries ◽  
Phase 1 ◽  
Permanent Teeth ◽  
Caries Experience ◽  
Tooth Structure ◽  
Health And Nutrition ◽  
Dmf Index ◽  
Oral Conditions ◽  
The Impact ◽  
Source Of Information

The DMF index provides one source of information on past and present dental caries experience; however, important limitations hinder its ability to characterize fully the impact of dental caries. The purpose of this paper is to describe a measure of selected restoration and tooth conditions that supplements information from the DMF index and to report on the application of this measure as part of the Third National Health and Nutrition Examination Survey, Phase 1, conducted between 1988 and 1991. Data from this survey were used to estimate the prevalence and severity of selected disaggregated physical and biological oral conditions among dentate adults aged 18 to 74 years. Trained, standardized, and calibrated dentist examiners assessed 28 permanent teeth or tooth spaces for each of 6,767 subjects. Teeth or tooth spaces were classified based on criteria for: defective intracoronal restorations, crowns, or bridges; gross loss of tooth structure associated with a restoration; pulpal involvement; or retained roots. Approximately 40.5%, or 61.6 million, dentate adults had at least one tooth or tooth space that met the criteria. Among all persons, an average of 0.9 teeth or tooth spaces met the criteria for at least one category. Adults with at least one scored tooth or tooth space had an average of 2.2 such teeth or tooth spaces. Data from this assessment supplement information available from the DMF index to provide a broader profile of the impact of dental caries on permanent teeth of US adults.

scholarly journals Language Learning Difficulties Reported by Beginner-Level Learners of Arabic Using Online Tools

2020 ◽  
Vol 11 ◽  
pp. 19-35
Author(s):  
Mahmoud Amer
Keyword(s):  
Language Learning ◽  
Learning Difficulties ◽  
Online Supplementary Material ◽  
Vocabulary Recall ◽  
Online Tools ◽  
Supplementary Material ◽  
Weekly Journal ◽  
Journal Entries

This study examined how two classes used online supplementary material to learn Arabic and the difficulties they reported in the process of their learning. The two classes have a total of 33 students who completed the course. The data from their weekly journal entries and log information from the site where the material was housed are used to describe the extent and the ways in which students used the material and issues they faced learning Arabic. Results show that students in both classes spent roughly 265 hours practicing Arabic with an average of 8 hours per student throughout the semester and that vocabulary recall and pronunciation were key struggles in their learning. Furthermore, this paper discusses some of the themes that emerged of students’ journal entries about their learning Arabic. Further implications are provided and discussed.

Trends in Caries Experience in US Employed Adults from 1971-74 To 1985: Cross-Sectional Comparisons

1993 ◽  
Vol 7 (1) ◽  
pp. 52-60 ◽  
Author(s):  
L.J. Brown ◽  
P.A. Swango
Keyword(s):  
Age Groups ◽  
Caries Experience ◽  
Dental Disease ◽  
Cross Sectional ◽  
Use Of Data ◽  
Dmf Index ◽  
The Us ◽  
Nhanes I

The evidence for trends in caries experience among adults is examined by use of data from the NCHS NHANES I survey of dental disease, conducted from 1971 to 1974, and the NIDR Survey of Employed Adults and Seniors, conducted in 1985 and 1986. The main findings of the study are: (1) Mean DMF teeth and surfaces have declined among US employed adults who were 18-44 years old in 1985 compared with similar-aged persons in 1971-74; (2) differences in mean DMF teeth and surfaces could not be detected when persons aged 45 or older were compared; (3) missing and decayed components of DMF decreased in all age groups; (4) mean DF teeth decreased in persons under 30 years of age and mean DF surfaces in persons under 35; (5) improvements in DMF were demonstrated by both genders and all regions of the US; (6) all tooth types (anteriors, premolars, and 1st and 2nd molars) showed improvement in DMF; and (7) while employed whites clearly demonstrated an improvement in DMF, a commensurate improvement among employed blacks was not apparent. As measured by the DMF index, caries experience declined in US employed adults under 45 years old between 1971-74 and 1985.

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