Bayesian Additive Regression Trees with Model Trees

Bayesian Additive Regression Trees (BART) is a tree-based machine learning method that has been successfully applied to regression and classification problems. BART assumes regularisation priors on a set of trees that work as weak learners and is very flexible for predicting in the presence of non-linearity and high-order interactions. In this paper, we introduce an extension of BART, called Model Trees BART (MOTR-BART), that considers piecewise linear functions at node levels instead of piecewise constants. In MOTR-BART, rather than having a unique value at node level for the prediction, a linear predictor is estimated considering the covariates that have been used as the split variables in the corresponding tree. In our approach, local linearities are captured more efficiently and fewer trees are required to achieve equal or better performance than BART. Via simulation studies and real data applications, we compare MOTR-BART to its main competitors. R code for MOTR-BART implementation is available at https://github.com/ebprado/MOTR-BART

Subjective burden and cultural motives for caregiving in informal caregivers of older people

Purpose: The aims of this study were to investigate variables related to cultural caregiving motives (obligation and reciprocity) and to analyze the relationship between these cultural caregiving motives and subjective burden in informal caregivers of disabled older people. Design and Methods: A secondary analysis of the last cross-sectional Spanish survey of informal caregivers of older people (n= 1,284, probability sample) was performed. Measurements included sociodemographic characteristics of caregivers (gender, age, relationship with care recipient, primary caregiver status, and duration of caregiving), intensity of care (hours per week, type of care, and number of activities of daily living [ADL] assisted), cultural motives for caregiving (obligation and balanced reciprocity), and caregiver subjective burden. Statistical analyses included descriptive (means, percentages, and 95% confidence intervals), bivariate (chi-square test), and multivariate (binary logistic regression) analyses. Findings: Obligation and reciprocity were higher in spouses than in other relatives and in nonrelatives and obligation increased with age as well as providing help with ADL. Balanced reciprocity was high in men. Obligation was not related with subjective burden, whereas balanced reciprocity was positively related. Conclusions: Reciprocity had a protective effect on subjective burden. No cultural differences have been found on this issue. Obligation may be a multidimensional concept that encompasses personal beliefs and social demands. Clinical Relevance: Balanced reciprocity is useful for early prevention and early intervention of subjective burden and must be included in nursing care plans for caregivers. Cultural factors support the comprehension of the caregiving process

Perceived needs of the family caregivers of people with dementia in a mediterranean setting: A qualitative study

The purpose of this study was to identify, classify and analyze the perceived needs of caregivers of elderly people with dementia during the care process. A descriptive phenomenological qualitative study using seven focus groups was conducted in different primary health care centers in the province of Jaén (Spain) between July 2012 and February 2013. Eighty-two family caregivers who were caring for people with dementia in different stages of the disease were selected by purposeful maximum variation sampling. Data were analyzed and organized thematically, considering the semantic and pragmatic content and field notes. Two main categories of the perceived needs of caregivers were identified. The first was related to the management of caring for a relative with dementia, and the second was related to the management of the caregivers’ own care. Our findings support the provision of comprehensive interventions for the improvement of caregivers’ emotional health that encompass more than one care need. This is where psycho-educational interventions aimed at managing the various aspects of dementia and self-care in caregivers can be accommodated. In addition, proactive interventions to develop important skills to care for a relative with dementia, which are not perceived as needs by the caregivers, are needed. These include skills in family negotiation, planning and searching for resources outside the family

lcc: an R package to estimate the concordance correlation, Pearson correlation and accuracy over time

Background and Objective: Observational studies and experiments in medicine, pharmacology and agronomy are often concerned with assessing whether different methods/raters produce similar values over the time when measuring a quantitative variable. This article aims to describe the statistical package lcc, for are, that can be used to estimate the extent of agreement between two (or more) methods over the time, and illustrate the developed methodology using three real examples. Methods: The longitudinal concordance correlation, longitudinal Pearson correlation, and longitudinal accuracy functions can be estimated based on fixed effects and variance components of the mixed-effects regression model. Inference is made through bootstrap confidence intervals and diagnostic can be done via plots, and statistical tests. Results: The main features of the package are estimation and inference about the extent of agreement using numerical and graphical summaries. Moreover, our approach accommodates both balanced and unbalanced experimental designs or observational studies, and allows for different within-group error structures, while allowing for the inclusion of covariates in the linear predictor to control systematic variations in the response. All examples show that our methodology is flexible and can be applied to many different data types. Conclusions: The lcc package, available on the CRAN repository, proved to be a useful tool to describe the agreement between two or more methods over time, allowing the detection of changes in the extent of agreement. The inclusion of different structures for the variance-covariance matrices of random effects and residuals makes the package flexible for working with different types of databases

Going beyond richness: Modelling the BEF relationship using species identity, evenness, richness and species interactions via the DImodels R package, and a comparison with traditional approaches

BEF studies aim at understanding how ecosystems respond to a gradient of species diversity. Diversity-Interactions models are suitable for analysing the BEF relationship. These models relate an ecosystem function response of a community to the identity of the species in the community, their evenness (proportions) and interactions. The no. of species in the community (richness) is also implicitly modelled through this approach. It is common in BEF studies to model an ecosystem function as a function of richness; while this can uncover trends in the BEF relationship, by definition, species diversity is much broader than richness alone, and important patterns in the BEF relationship may remain hidden. We compare DI models to traditional modelling approaches to highlight the advantages of using a multi-dimensional definition of species diversity. DI models can capture variation due to species identities, species proportions and species interactions, in addition to richness effects. We also introduce the DImodels R package for implementing DI models. Through worked examples, we show that using DI models can lead to considerably improved model fit over other methods. Collapsing the multiple dimensions of species diversity to a single dimension (such as richness) can result in valuable ecological information being lost. Predicting from a DI model is not limited to the study design points, the model can extrapolate to predict for any species composition and proportions. Overall, DI models lead to enhanced inference compared to other approaches. Expressing the BEF relationship as a function of richness alone can be useful to capture overall trends, however, there are multiple ways to quantify the species diversity of a community. DI modelling provides a framework to test the multiple aspects of species diversity and facilitates uncovering a deeper ecological understanding of the BEF relationship

Correlates of Burden in Primary Caregivers of Older Relatives: A Cross-sectional Study

PURPOSE: To analyze the effect of cultural factors on the subjective burden of primary home caregivers of older relatives. DESIGN: Cross-sectional study. Primary home caregivers (N = 208) of older relatives were recruited in Spain using systematic random sampling. METHODS: The data were collected in 2010 through interviews. The measures included sociodemographic characteristics, stressors (the intensity of care provided and the care-recipient's needs; the latter were assessed using the Barthel Index, the Pfeiffer Short Portable Mental Status Questionnaire and the Cummings Neuropsychiatric Inventory), cultural factors (kinship ties, common residence, perceived social support, and cultural motives for caregiving), and caregiver subjective burden (Caregiver Strain Index). The data were analyzed using bivariate procedures and multiple linear regression. FINDINGS: After controlling for caregiver age, caregiver gender, stressors, and duration of caregiving, subjective burden was negatively associated with perceived social support and reciprocity, and in the subgroup of adult children, it was positively associated with common residence. Cultural factors explained 29% of the variance in burden. CONCLUSIONS: Our findings add to the existing evidence regarding the influence of cultural factors in the perception of burden in caregiving situations. CLINICAL RELEVANCE: A risk profile could be proposed for subjective burden in primary family caregivers. Individuals who are at risk are characterized as young, offspring who live with the care recipient, care for a care recipient with behavioral problems, are unsatisfied with the social support received, and have a low balanced reciprocity

2007 Symposium Announcement

The fungal genera Metarhizium and Beauveria are considered as both entomopathogens and endophytes; they are able to colonize a wide variety of plants and can cause increased plant growth and protect plants against pests. In view of the need for new biological methods for plant protection and how promising and little studied candidates entomopathogens are, the aim of this research was to evaluate the potential of two isolates of Metarhizium robertsii (ESALQ 1622) and Beauveria bassiana (ESALQ 3375) to suppress spider mite Tetranychus urticae population growth and ability to promote growth of bean plants Phaseolus vulgaris after seed treatment, in order to develop an innovative strategy by using these fungi as inoculants to improve both spider mites control and plant growth and yield. In addition, behavioral responses and predation rates of the predatory mite Phytoseiulus persimilis towards fungal treated plants and spider mites from these plants were also evaluated in leaf disc assays to assess potential conflicting effects of the fungal inoculations on overall pest control at higher trophic levels. Seed inoculations by the two isolates of M. robertsii and B. bassiana were done individually and in combinations to evaluate potential benefits of co-inoculants. The results showed a significant reduction in T. urticae populations and improved plant development when inoculated with M. robertsii and B. bassiana individually and in combination. The predatory mite P. persimilis showed no difference in the predation rate on T. urticae from treated and untreated plants even though the predators were most likely to feed on spider mites from fungal treated plants during the first half of the trial, and on spider mites from control plants during the remainder of the trial. Overall, the two fungal isolates have potential as seed inoculants to suppress spider mites in bean and the strategy appears to have no conflict with use of predatory mites. Co-inoculation of both fungal isolates showed no additional benefits compared to single isolate applications under the given test conditions