Feasible estimation of generalized linear mixed models (GLMM) with weak dependency between groups

This paper presents a two-step pseudo likelihood estimation technique for generalized linear mixed models with the random effects being correlated between groups. The core idea is to deal with the intractable integrals in the likelihood function by multivariate Taylor's approximation. The accuracy of the estimation technique is assessed in a Monte-Carlo study. An application of it with a binary response variable is presented using a real data set on credit defaults from two Swedish banks. Thanks to the use of two-step estimation technique, the proposed algorithm outperforms conventional pseudo likelihood algorithms in terms of computational time.

Hglm: A package for fitting hierarchical generalized linear models

We present the hglm package for fitting hierarchical generalized linear models. It can be used for linear mixed models and generalized linear mixed models with random effects for a variety of links and a variety of distributions for both the outcomes and the random effects. Fixed effects can also be fitted in the dispersion part of the model.

Genetic heterogeneity of residual variance : estimation of variance components using double hierarchical generalized linear models

Background: The sensitivity to microenvironmental changes varies among animals and may be under genetic control. It is essential to take this element into account when aiming at breeding robust farm animals. Here, linear mixed models with genetic effects in the residual variance part of the model can be used. Such models have previously been fitted using EM and MCMC algorithms. Results: We propose the use of double hierarchical generalized linear models (DHGLM), where the squared residuals are assumed to be gamma distributed and the residual variance is fitted using a generalized linear model. The algorithm iterates between two sets of mixed model equations, one on the level of observations and one on the level of variances. The method was validated using simulations and also by re-analyzing a data set on pig litter size that was previously analyzed using a Bayesian approach. The pig litter size data contained 10,060 records from 4,149 sows. The DHGLM was implemented using the ASReml software and the algorithm converged within three minutes on a Linux server. The estimates were similar to those previously obtained using Bayesian methodology, especially the variance components in the residual variance part of the model. Conclusions: We have shown that variance components in the residual variance part of a linear mixed model can be estimated using a DHGLM approach. The method enables analyses of animal models with large numbers of observations. An important future development of the DHGLM methodology is to include the genetic correlation between the random effects in the mean and residual variance parts of the model as a parameter of the DHGLM.

Actitudes hacia la variedad caló y sus hablantes : Un estudio sociolingüístico de las opiniones de adolescentes andaluces

Caló is a language/variety spoken by the Spanish Calé (i.e. the Roma). The variety belongs to a group oflanguages referred to as “Para-Romani”, characterized by Romani vocabulary, but largely non-Romani morphology, phonology and syntax, in the case of Caló deriving from Spanish. Much research has been carried out regarding the vocabulary and the grammar of this variety.The conclusions drawn in those studies indicate that Caló is on its way to extinction. However, thereis an expressed interest in reintroducing the variety, in a form called “Romanó-Caló”. Language attitudes play a decisive role for the destiny of endangered languages. In order for arevitalization project to be successful, the attitudes towards the variety being reintroduced have to bepositive. The aim of this study is to measure the attitudes that both Calé and non-Calé have towards Calóand Caló speakers, a type of study never carried out in the past. The methods applied are both direct andindirect. In part one, 231 informants listened to different recordings of voices acting as either a “Spanishspeaking person” or a “Caló speaking person”, a technique referred to as ‘matched guise’. Firstly,the informants were asked to write down their first three impressions of the speakers. Secondly, nineshort questions related to the voices were asked, to which the subjects expressed their answers on attitudescales. They were also asked to match the voices with photos of people. Furthermore, theinformants have answered questions regarding what variety is spoken at home, as well as if he or she hasany knowledge of, or contact with, any language/variety, apart from Spanish. 182 informants continuedwith part two of the questionnaire, which consisted of 20 items – positive and negative statementstowards Caló and Caló speakers. The informants have rated their agreement or disagreement to thesestatements on a Likert scale. Another exercise measured the willingness of the informants to use Calówords for naming various objects. In addition, the subjects were tested on their knowledge of some Calówords, as well as asked whether they thought it was “useful” to know how to speak Caló. Variousstatistical methods have been used in order to establish whether or not the results are statisticallysignificant. The results of the analysis indicate that the attitudes differ towards Caló and Calóspeakers, depending on the informant’s (a) ethnicity (b) contact with Caló as well as with Calóspeakers, and (c) gender. It is those who – in their own opinion – belong to the ethnic group Calé, as wellas those who claim that they have some contact with the variety and its speakers, who show positiveattitudes in both parts of the study. The women also show more positive attitudes than the men. It is alsopossible to note positive attitudes towards the variety and its speakers among the subjects with a highlevel of knowledge of Caló words, as well as among those with the highest willingness to use Caló. These observations suggest that a revitalization project of the variety Caló has a clear chance ofbeing successful.

The fall descriptions and health characteristics of older adults with hip fracture : a mixed methods study

Background: In light of the multifactorial etiology of fall-related hip fracture, knowledge of fall circumstances may be especially valuable when placed in the context of the health of the person who falls. We aimed to investigate the circumstances surrounding fall-related hip fractures and to describe fall circumstances in relation to participants' health and functional characteristics. Methods: The fall circumstances of 125 individuals (age >= 50 years) with hip fracture were investigated using semi-structured interviews. Data concerning participants' health (comorbidities and medications) and function (self-reported performance of mobility, balance, personal activities of daily living and physical activity, previous falls and hand grip strength) were collected via medical records, questionnaires and dynamometry. Using a mixed methods design, both data sets were analysed separately and then merged in order to provide a comprehensive description of fall events and identify eventual patterns in the data. Results: Fall circumstances were described as i) Activity at the time of the fall: Positional change (n = 24, 19%); Standing (n = 16, 13%); Walking (n = 71, 57%); Balance challenging (n = 14, 11%) and ii) Nature of the fall: Environmental (n = 32, 26%); Physiological (n = 35, 28%); Activity-related indoor (n = 8, 6%) and outdoor (n = 8, 6%); Trips and slips on snow (n = 20, 16%) and in snow-free conditions (n = 12, 10%) and Unknown (n = 10, 8%). We observed the following patterns regarding fall circumstances and participants' health: those who fell i) during positional change had the poorest functional status; ii) due to environmental reasons (indoors) had moderate physical function, but high levels of comorbidity and fall risk increasing medications; iii) in snow-free environments (outdoors) appeared to have a poorer health and functional status than other outdoor groups. Conclusions: Our findings indicate that patterns exist in relation to the falls circumstances and health characteristics of people with hip fracture which build upon that previously reported. These patterns, when verified, can provide useful information as to the ways in which fall prevention strategies can be tailored to individuals of varying levels of health and function who are at risk for falls and hip fracture.