DSpace Angular :: Browsing by Author "Alvares, Danilo"

Browsing by Author "Alvares, Danilo"

Now showing 1 - 20 of 20

A new flexible Bayesian hypothesis test for multivariate data
(2023) Gutierrez, Ivan; Gutierrez, Luis; Alvares, Danilo
We propose a Bayesian hypothesis testing procedure for comparing the multivariate distributions of several treatment groups against a control group. This test is derived from a flexible model for the group distributions based on a random binary vector such that, if its jth element equals one, then the jth treatment group is merged with the control group. The group distributions' flexibility comes from a dependent Dirichlet process, while the latent vector prior distribution ensures a multiplicity correction to the testing procedure. We explore the posterior consistency of the Bayes factor and provide a Monte Carlo simulation study comparing the performance of our procedure with state-of-the-art alternatives. Our results show that the presented method performs better than competing approaches. Finally, we apply our proposal to two classical experiments. The first one studies the effects of tuberculosis vaccines on multiple health outcomes for rabbits, and the second one analyzes the effects of two drugs on weight gain for rats. In both applications, we find relevant differences between the control group and at least one treatment group.
A Proposal of Model of Emotional Regulation in Intelligent Learning Environments
(VILNIUS UNIV, INST MATHEMATICS & INFORMATICS, 2021) Reis, Helena Macedo; Alvares, Danilo; Jaques, Patricia A.; Isotani, Seiji
Emotions can influence cognitive development and are key elements to the teaching-learning process. Positive emotions (e.g., engagement) can improve the ability to solve problems, store information, and make decisions. On the other hand, negative emotions (e.g., boredom) reduce the capacity to process information at a deeper level, preventing learning to become effective. Therefore, students' emotions must be regulated to hinder negative and to promote positive emotions during learning. To support the choice of the best intervention to regulate individual emotions, this article proposes an algorithm based on simulated data considering different individual performances in solving Algebra exercises. The results suggest that the proposed model has high success rates (over 90%) in the choice of interventions and may be applied in real scenarios.
A Two-Stage Approach for Bayesian Joint Models of Longitudinal and Survival Data: Correcting Bias with Informative Prior
(2021) Leiva-Yamaguchi, Valeria; Alvares, Danilo
Joint models of longitudinal and survival outcomes have gained much popularity in recent years, both in applications and in methodological development. This type of modelling is usually characterised by two submodels, one longitudinal (e.g., mixed-effects model) and one survival (e.g., Cox model), which are connected by some common term. Naturally, sharing information makes the inferential process highly time-consuming. In particular, the Bayesian framework requires even more time for Markov chains to reach stationarity. Hence, in order to reduce the modelling complexity while maintaining the accuracy of the estimates, we propose a two-stage strategy that first fits the longitudinal submodel and then plug the shared information into the survival submodel. Unlike a standard two-stage approach, we apply a correction by incorporating an individual and multiplicative fixed-effect with informative prior into the survival submodel. Based on simulation studies and sensitivity analyses, we empirically compare our proposal with joint specification and standard two-stage approaches. The results show that our methodology is very promising, since it reduces the estimation bias compared to the other two-stage method and requires less processing time than the joint specification approach.
Amerindian ancestry proportion as a risk factor for inflammatory bowel diseases: results from a Latin American Andean cohort
(2023) Pérez Jeldres, Tamara De Lourdes; Magne, Fabien; Ascui, Gabriel; Alvares, Danilo; Orellana, Matias; Álvarez Lobos Manuel Marcelo; Hernández Rocha, Cristián Antonio; Azocar, Lorena; Aguilar, Nataly; Espino, Alberto; Estela, Ricardo; Escobar, Sergio; Zazueta, Alejandra; Baez, Pablo; Silva, Veronica; de la Vega, Andres; Arriagada, Elizabeth; Pávez Ovalle, Carolina Denisse; Diaz-Asencio, Alejandro; Travisany, Dante; Miquel Poblete, Juan Francisco; Villablanca, Eduardo J.; Kronenberg, Mitchell; Bustamante, Maria Leonor
Background and aimsLatin American populations remain underrepresented in genetic studies of inflammatory bowel diseases (IBDs). Most genetic association studies of IBD rely on Caucasian, African, and Asian individuals. These associations have yet to be evaluated in detail in the Andean region of South America. We explored the contribution of IBD-reported genetic risk variants to a Chilean cohort and the ancestry contribution to IBD in this cohort.MethodsA total of 192 Chilean IBD patients were genotyped using Illumina's Global Screening Array. Genotype data were combined with similar information from 3,147 Chilean controls. The proportions of Aymara, African, European, and Mapuche ancestries were estimated using the software ADMIXTURE. We calculated the odds ratios (ORs) and 95% confidence intervals (CIs) for gender, age, and ancestry proportions. We also explored associations with previously reported IBD-risk variants independently and in conjunction with genetic ancestry.ResultsThe first and third quartiles of the proportion of Mapuche ancestry in IBD patients were 24.7 and 34.2%, respectively, and the corresponding OR was 2.30 (95%CI 1.52-3.48) for the lowest vs. the highest group. Only one variant (rs7210086) of the 180 reported IBD-risk SNPs was associated with IBD risk in the Chilean cohort (adjusted P = 0.01). This variant is related to myeloid cells.ConclusionThe type and proportion of Native American ancestry in Chileans seem to be associated with IBD risk. Variants associated with IBD risk in this Andean region were related to myeloid cells and the innate immune response.
Bayesian modeling for pro-environmental behavior data: sorting and selecting relevant variables
(2022) Reveco-Quiroz, Paula; Sandoval-Diaz, Jose; Alvares, Danilo
Pro-environmental behaviors towards climate change can be measured and evaluated in different fields. Typically, surveys are the standard tool for extracting personal information regarding this phenomenon. However, statistical modeling for these surveys is not straightforward, as the response variable is often not explicit. Hence, we propose a set of methodological procedures to deal with pro-environmental behavior data. First, validity evidence through a factorial analysis. Second, indexes are created from factor scores, where one of the latent factors summarizes a target variable. Third, a Beta regression is used to model the index of interest. Fourth, the inferential process is performed from a Bayesian perspective, in which posterior probabilities are used to sort and select the relevant variables. Finally, suitable models are obtained, and conclusions can be drawn from them. As a motivation, we used data from two Chilean surveys to illustrate our methodology as well as interpret and discuss the results.
Bayesian regularization for flexible baseline hazard functions in Cox survival models
(WILEY, 2021) Lazaro, Elena; Armero, Carmen; Alvares, Danilo
Fully Bayesian methods for Cox models specify a model for the baseline hazard function. Parametric approaches generally provide monotone estimations. Semi-parametric choices allow for more flexible patterns but they can suffer from overfitting and instability. Regularization methods through prior distributions with correlated structures usually give reasonable answers to these types of situations. We discuss Bayesian regularization for Cox survival models defined via flexible baseline hazards specified by a mixture of piecewise constant functions and by a cubic B-spline function. For those "semi-parametric" proposals, different prior scenarios ranging from prior independence to particular correlated structures are discussed in a real study with microvirulence data and in an extensive simulation scenario that includes different data sample and time axis partition sizes in order to capture risk variations. The posterior distribution of the parameters was approximated using Markov chain Monte Carlo methods. Model selection was performed in accordance with the deviance information criteria and the log pseudo-marginal likelihood. The results obtained reveal that, in general, Cox models present great robustness in covariate effects and survival estimates independent of the baseline hazard specification. In relation to the "semi-parametric" baseline hazard specification, the B-splines hazard function is less dependent on the regularization process than the piecewise specification because it demands a smaller time axis partition to estimate a similar behavior of the risk.
Bayesian variable selection and survival modeling: assessing the Most important comorbidities that impact lung and colorectal cancer survival in Spain
(2022) Javier Rubio, Francisco; Alvares, Danilo; Redondo-Sanchez, Daniel; Marcos-Gragera, Rafael; Sanchez, Maria-Jose; Angel Luque-Fernandez, Miguel
Cancer survival represents one of the main indicators of interest in cancer epidemiology. However, the survival of cancer patients can be affected by several factors, such as comorbidities, that may interact with the cancer biology. Moreover, it is interesting to understand how different cancer sites and tumour stages are affected by different comorbidities. Identifying the comorbidities that affect cancer survival is thus of interest as it can be used to identify factors driving the survival of cancer patients. This information can also be used to identify vulnerable groups of patients with comorbidities that may lead to worst prognosis of cancer. We address these questions and propose a principled selection and evaluation of the effect of comorbidities on the overall survival of cancer patients. In the first step, we apply a Bayesian variable selection method that can be used to identify the comorbidities that predict overall survival. In the second step, we build a general Bayesian survival model that accounts for time-varying effects. In the third step, we derive several posterior predictive measures to quantify the effect of individual comorbidities on the population overall survival. We present applications to data on lung and colorectal cancers from two Spanish population-based cancer registries. The proposed methodology is implemented with a combination of the R-packages mombf and rs tan. We provide the code for reproducibility at https://github.com/migariane/BayesVarlmpComorbiCancer.
Developing Critical Thinking in Technical and Vocational Education and Training
(Taylor and Francis, 2023) Lopez, Felipe; Contreras, Mayra; Nussbaum, Miguel; Paredes, Ricardo; Gelerstein, Damian; Alvares, Danilo; Chiuminatto Munoz Pablo Andres
Critical thinking has been difficult to develop in technical and vocational education and training, where acquiring practical skills is often the priority. This study looks at whether tried-and-tested methods for developing critical thinking in higher education are also effective in this educational context. To test this, an intervention was carried out as part of a compulsory, semester-long "Basic Communication Skills" class for 149 first year engineering students. This involved linking the expected learning outcomes for the course to a series of sub-skills comprising an updated definition of critical thinking. Furthermore, a set of strategies promoting active participation among students was also implemented. The proposed methodology led to improved levels of critical thinking when compared to traditional teaching methods. It was found that lessons characterized as interactive, dynamic, and encouraging active student participation facilitate the teacher's job in the classroom and improve the development of critical thinking in a specific technical and vocational education context.
Enhancing Grit and Critical Thinking in Rural Primary Students: Impact of a Targeted Educational Intervention
(2024) Gallardo-Estrada, Carla; Nussbaum, Miguel; Pinto, Mauricio; Alvares, Danilo; Alario-Hoyos, Carlos
This study examined the impact of a targeted educational intervention on enhancing grit and critical thinking skills among 10-year-old primary school students in rural Chile. The intervention, involving 153 students from six public schools, used a language classroom model with structured reading activities. Grit and critical thinking were measured pre- and post-intervention. Results showed improvements in the intervention group. The intervention's effectiveness was consistent across genders. The findings suggest that structured, student-centered educational strategies can enhance grit and critical thinking in primary students. Further research is needed to generalize the results to different settings and age groups.
Ethnicity influences phenotype and clinical outcomes: Comparing a South American with a North American inflammatory bowel disease cohort
(2022) Perez-Jeldres, Tamara; Pizarro, Benjamin; Ascui, Gabriel; Orellana, Matias; Cerda-Villablanca, Mauricio; Alvares, Danilo; de la Vega, Andres; Cannistra, Macarena; Cornejo, Barbara; Baez, Pablo; Silva, Veronica; Arriagada, Elizabeth; Rivera-Nieves, Jesus; Estela, Ricardo; Hernandez-Rocha, Cristian; alvarez-Lobos, Manuel; Tobar, Felipe
Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn disease (CD), has emerged as a global disease with an increasing incidence in developing and newly industrialized regions such as South America. This global rise offers the opportunity to explore the differences and similarities in disease presentation and outcomes across different genetic backgrounds and geographic locations. Our study includes 265 IBD patients. We performed an exploratory analysis of the databases of Chilean and North American IBD patients to compare the clinical phenotypes between the cohorts. We employed an unsupervised machine-learning approach using principal component analysis, uniform manifold approximation, and projection, among others, for each disease. Finally, we predicted the cohort (North American vs Chilean) using a random forest. Several unsupervised machine learning methods have separated the 2 main groups, supporting the differences between North American and Chilean patients with each disease. The variables that explained the loadings of the clinical metadata on the principal components were related to the therapies and disease extension/location at diagnosis. Our random forest models were trained for cohort classification based on clinical characteristics, obtaining high accuracy (0.86 = UC; 0.79 = CD). Similarly, variables related to therapy and disease extension/location had a high Gini index. Similarly, univariate analysis showed a later CD age at diagnosis in Chilean IBD patients (37 vs 24; P = .005). Our study suggests a clinical difference between North American and Chilean IBD patients: later CD age at diagnosis with a predominantly less aggressive phenotype (39% vs 54% B1) and more limited disease, despite fewer biological therapies being used in Chile for both diseases.
Integrating a collaboration script and group awareness to support group regulation and emotions towards collaborative problem solving
(Taylor and Francis, 2022) Rojas, Matias; Nussbaum, Miguel; Guerrero, Orlando; Chiuminatto Munoz Pablo Andres; Greiff, Samuel; Del Rio, Rodrigo; Alvares, Danilo
The research landscape displays increasing awareness of the important role of self-regulation and emotions in the process of acquiring Collaborative Problem-Solving skills (CPS), which are considered essential in almost all areas of life. However, there is still a dearth of research on developing CPS skills among elementary-school students. Our research therefore looks at how elementary school students' regulation skills and emotions are supported by a collaborative game using a collaboration script to scaffold group awareness. An intervention was carried out with a sample of 223 students aged between 10 and 13. The experimental group worked collaboratively in sub-groups, scaffolded by the game, while the control group attended regular lessons. The students' attitudes towards collaboration were evaluated before and after the intervention. In addition to this, a focus group was held a week after the intervention, which involved 32 students from both groups. The quantitative analysis revealed that attitudes towards collaboration improved significantly among students in the experimental group. This difference can be explained by a combination of the intervention, the students' initial attitudes, and their respective GPAs. The qualitative analysis provided evidence of the regulation processes and emotions that emerge when combining a collaboration script with group awareness tools during CPS activities. Furthermore, the results highlighted the relationship between these tools and positive emotions (i.e., satisfaction), co-regulation, and shared regulation. These findings suggest that there is a relationship between the co-regulation process required by the game and a shift in emotions from frustration to satisfaction. This work provides evidence of how scaffolding group awareness using a collaboration script supports regulation skills and emotions, thus promoting the development of Collaborative Problem-Solving skills.
Is Teamwork Different Online Versus Face-to-Face? A Case in Engineering Education
(2020) Goñi, Julian ; Cortázar, Catalina; Alvares, Danilo ; Donoso, Uranía ; Miranda, Constanza
Teamwork has been systematically studied in engineering education as an educational method and a learning outcome. Based on the recent advances in socially-shared regulation as a framework for teamwork processes, this study explores the impact of the transition to online learning. The purpose of this study is to understand if face-to-face and online team dynamics differ concerning the prevalence of personal goals, team challenges, and individual/social strategies. The Adaptive Instrument for Regulation of Emotions (AIRE) Questionnaire was used to compare two semesters in project-based learning engineering courses that were face-to-face (2019) and then converted to an online modality (2020) due to the COVID-19 crisis. Our results show that both modalities report mostly the same prevalence of goals, challenges, and strategies. However, online students tend to manifest a significantly lower prevalence of specific challenges and strategies, suggesting that online teamwork may have involved less group deliberation. These results provide evidence for the "equivalency theory" between online and face-to-face learning in a context where all systemic levels transitioned to a digital modality. These findings raise the question of whether online teaching encourages the emergence of team conflict and deliberation needed for creative thinking.
New insights from GWAS on BMI-related growth traits in a longitudinal cohort of admixed children with Native American and European ancestry
(CELL PRESS, 2023) Vicuña, Lucas; Barrientos, Esteban; Norambuena, Tomás; Alvares, Danilo; Gana Ansaldo, Juan Cristóbal; Leiva Yamaguchi, Valeria; Meza, Cristian; Lorenzoni Santos, José Guillermo; Mericq, Verónica; Pereira, Ana; Eyheramendy, Susana
Body-mass index (BMI) is a hallmark of adiposity. In contrast with adulthood, the genetic architecture of BMI during childhood is poorly understood. The few genome-wide association studies (GWAS) on children have been performed almost exclusively in Europeans and at single ages. We performed cross-sectional and longitudinal GWAS for BMI-related traits on 904 admixed children with mostly Mapuche Native American and European ancestries. We found regulatory variants of the immune gene HLA-DQB3 strongly associated with BMI at 1.5 - 2.5 years old. A variant in the sex-determining gene DMRT1 was associated with the age at adiposity rebound (Age-AR) in girls (P = 9.8 x 10(-9)). BMI was significantly higher in Mapuche than in Europeans between 5.5 and 16.5 years old. Finally, Age-AR was significantly lower (P = 0.004) by 1.94 years and BMI at AR was significantly higher (P = 0.04) by 1.2 kg/m(2), in Mapuche children compared with Europeans.
Promoting critical thinking in an online, project-based course
(2021) Cortazar, Catalina; Nussbaum, Miguel; Harcha, Jorge; Alvares, Danilo; Lopez, Felipe; Goni, Julian; Cabezas, Veronica
Education institutions are expected to contribute to the development of students? critical thinking skills. Due to COVID-19, there has been a surge in interest in online teaching. The aim of this study is therefore to design a strategy to promote critical thinking in an online setting for first year undergraduates. An intervention was carried out with 834 students at an engineering school; it comprised five activities designed to develop critical thinking. Both the control and experimental groups worked with a project-based learning strategy, while the experimental group was provided with scaffolding for a socially shared regulation process. All students answered an identical pre-and post-test so as to analyze the impact on critical thinking. Both strategies performed significantly better on the post-test, suggesting that online project-based learning improves critical thinking. However, following a socially shared regulation scaffolding led to a significantly greater improvement. In this sense, the socially shared regulation scaffolding provided to the experimental group proved to be key, while feedback was also an important element in the development of critical thinking. This study shows that online project-based learning fosters the development of critical thinking, while providing a socially shared regulation scaffolding also has a significant impact.
Relationship between marital status and incidence of type 2 diabetes mellitus in a Brazilian rural population: The Baependi Heart Study
(2020) de Oliveira, Camila Maciel; Viater Tureck, Luciane; Alvares, Danilo; Liu, Chunyu; Horimoto, Andrea Roseli Vancan Russo; Balcells, Mercedes; de Oliveira Alvim, Rafael; Krieger, Jose Eduardo; Pereira, Alexandre Costa
Many factors influence the incidence of type 2 diabetes mellitus (T2DM). Here, we investigated the associations between socio-demographic characteristics and familial history with the 5-year incidence of T2DM in a family-based study conducted in Brazil. T2DM was defined as baseline fasting blood glucose >= 126 mg/dL or the use of any hypoglycaemic drug. We excluded individuals with T2DM at baseline or if they did not attend two examination cycles. After exclusions, we evaluated a sample of 1,125 participants, part of the Baependi Heart Study (BHS). Mixed-effects logistic regression models were used to assess T2DM incident given different characteristics. At the 5-year follow-up, the incidence of T2DM was 6.7% (7.2% men and 6.3% women). After adjusting for age, sex, and education status, the model that combined marital and occupation status, skin color, and familial history of T2DM provided the best prediction for T2DM incidence. Only marital status was independently associated with T2DM incidence. Individuals that remained married, despite having significantly increased their weight, were significantly less likely to develop diabetes than their divorced counterparts.
SemiCompRisks: An R Package for the Analysis of Independent and Cluster-correlated Semi-competing Risks Data
(2019) Alvares, Danilo; Haneuse, Sebastien; Lee, Catherine; Lee, Kyu Ha
Semi-competing risks refer to the setting where primary scientific interest lies in estimation and inference with respect to a non-terminal event, the occurrence of which is subject to a terminal event. In this paper, we present the R package SemiCompRisks that provides functions to perform the analysis of independent/clustered semi-competing risks data under the illness-death multi-state model. The package allows the user to choose the specification for model components from a range of options giving users substantial flexibility, including: accelerated failure time or proportional hazards regression models; parametric or non-parametric specifications for baseline survival functions; parametric or non-parametric specifications for random effects distributions when the data are cluster-correlated; and, a Markov or semi-Markov specification for terminal event following non-terminal event. While estimation is mainly performed within the Bayesian paradigm, the package also provides the maximum likelihood estimation for select parametric models. The package also includes functions for univariate survival analysis as complementary analysis tools.
Sequential Monte Carlo methods in Bayesian joint models for longitudinal and time-to-event data
(2021) Alvares, Danilo; Armero, Carmen; Forte, Anabel; Chopin, Nicolas
The statistical analysis of the information generated by medical follow-up is a very important challenge in the field of personalized medicine. As the evolutionary course of a patient's disease progresses, his/her medical follow-up generates more and more information that should be processed immediately in order to review and update his/her prognosis and treatment. Hence, we focus on this update process through sequential inference methods for joint models of longitudinal and time-to-event data from a Bayesian perspective. More specifically, we propose the use of sequential Monte Carlo (SMC) methods for static parameter joint models with the intention of reducing computational time in each update of the full Bayesian inferential process. Our proposal is very general and can be easily applied to most popular joint models approaches. We illustrate the use of the presented sequential methodology in a joint model with competing risk events for a real scenario involving patients on mechanical ventilation in intensive care units (ICUs).
The impacts of scaffolding socially shared regulation on teamwork in an online project-based course
(2022) Cortazar, Catalina; Nussbaum, Miguel; Alario-Hoyos, Carlos; Goni, Julian; Alvares, Danilo
Employers now consider teamwork one of the essential skills for students to acquire during their academic life. However, COVID-19 has accelerated the transition towards online learning, affecting how we work in teams. This study looked at how scaffolding socially shared regulation of learning can influence teamwork in an online, project-based course. Intra-group peer assessment was used to analyze three variables during a first-year engi-neering course. By following the proposed scaffolding, students found an optimum balance in their contribution to team meetings. They also managed to establish a positive working environment earlier in the semester. This study contributes to the field by showing that scaffolding socially shared regulation in an online, project-based course allows for an interplay between collaboration during class and cooperation outside of it. This interplay ultimately leads teams to achieve better results on their final project.
The Use of Physically Active Academic Lessons During the Transition to Face-to-Face Classes
(2024) Beserra, Vagner; Nussbaum, Miguel; Navarrete, Monica; Garrido, Norman; Alvares, Danilo
Schools are pivotal stakeholders in increasing the amount of student physical activity, an attribution especially relevant while the COVID-19 pandemic is not overcome. This article evaluates how the use of physically active academic lessons impacted mathematics learning and the amount of physical activity during the transition to face-to-face classes. The objective was also to analyze students, parents, and teachers' perceptions of this experience. Therefore, for at least 6 weeks in mid-2021, 290 Chilean elementary school students from different schools, together with their 11 teachers, learned and practiced a choreography on geometry during the school routine. Both quantitative and qualitative instruments were used to evaluate this experience. The results from the pre- and post-test showed that students increased their geometry scores significantly (Z = 13.116, p < .001) by an average of 24.28 percentage points with an increase of 7.33 percentage points if the student attended face-to-face classes. Moreover, the results of the focus groups revealed a positive perception of the experience and increased physical activity. Overall, the study suggests that incorporating physically active academic lessons positively affect both academic performance and students' physical activity levels during the transition to face-to-face classes.
What to Learn? Socialization of the Subject Hierarchy in Schools
(2021) Araneda, Daniel; Galarce, Jeremy; Alvares, Danilo; Nussbaum, Miguel
The role of the school curriculum is in tension with two points: socializing the essential knowledge needed for life and reflecting the inequalities of society. The present study looks at the effectiveness of this socialization by comparing learner interests with the national curriculum. 442 10th grade students in Chile were divided into 4 groups based on their socioeconomic status and academic achievement. The students were asked to design two ideal school timetables: one reflecting their interests, and one showing what they feel is relevant for their future. The results reveal that student interests differ considerably from the national curriculum. However, when students design a timetable based on their future it tends to resemble the curriculum much more closely. Socioeconomic status proved not to be particularly relevant. On the other hand, gender appears to be the most significant variable when explaining these differences.

Browsing by Author "Alvares, Danilo"

Results Per Page

Sort Options