A mixture model with application to discrete competing risks data

In this paper, we modify the continuous time mixture competing risks model (Larson and Dinse, 1985) to handle discrete competing risks data. The main result of the model is an alternate regression expression for the cumulative incidence function. The structure of the regression expression for the cumulative incidence function under this model, and the proportional hazards assumption for the conditional hazard rates with piece-wise constant baseline conditional hazards, combine to allow for another means to assess the covariate effects on the cumulative incidence function. This benefit comes at some computational costs because the parameters are estimated via an EM algorithm. The proposed model is applied to real data and it is found that it improves the exercise of evaluating the covariate effects on the cumulative incidence function compared to other discrete competing risks models

Analysis of attrition and retention rates using the generalized linear model

Improving the progression rates of students and reducing the numbers of students dropping out from institutions of higher education are critical to get maximum return for financial subsidies received or private fees paid, as well as being key components for producing skilled workers within the developing economy. Institutions of higher education in South Africa are accordingly grappling with finding a delicate balance between access, equity, redress and quality. A study of attrition is a sensitive, yet essential issue for university planning offices. An appropriate modelling approach is essential for identifying factors that contribute to attrition. This study presents two models for attrition, with slow and fast drifts of attrition, as students progress from year to year, with constant and varying dampening effects. The fast dampening model has the property of relative risk, whilst the slow drifting model has the property of odds ratio. The effect of faculty, gender, race and entry batch year, on the progression and attrition rates was examined in the study. The results of the analysis show that the first year attrition rate of White students is higher than that of the other race groups, whilst the retention and graduation rates of White students, is much greater than that of the Black and Indian students, from second year onwards. Throughout the three-year study period, the attrition rates of female students was found to be consistently lower than the corresponding attrition rates of male students

Fitting three parameter growth curves using a nonlinear mixed effects modelling approach

A nonlinear mixed modelling approach was applied to model individual tree diameter increment using three nonlinear growth functions for Eucalyptus tree plantations. The objective of the study is to develop a stem radial increment model for two clones of Eucalyptus tree, and compare their growth potential. Three nonlinear growth curves (Gompertz, logistic and asymptotic regression) were fitted to stem radius data. Estimations of parameters were made using the approximate likelihood functions. The estimators obtained from these approximate likelihood function are a combination of least squares estimators for nonlinear mixed effects models and maximum likelihood estimators from linear mixed effects models. The asymptotic regression model with three random effects appears well suited to represent the random effect covariance structure. The heterogeneous variance model that varies with tree age is found to be suitable model that characterize the within tree error variability. Clone has a significant effect on the asymptote of the asymptotic regression curve. The analysis suggests that GU clone on the average has a larger stem radial measurement than the GC clone during the entire juvenile stage

Joint Modeling of Poverty of Households and Malnutrition of Children Under Five Years from Demographic and Health Survey Data: Case of Rwanda

The main objective of this study was to identify the risk factors associated to malnutrition of children under five years and poverty and assess the correlation between them. We created a composite index from three anthropometric indictors (stunting, underweight and wasting).A multivariate joint model using the generalized linear mixed model was utilized for the analyses of the data. Child age, birth order of the children, the gender of children, birth weights of the children, multiple birth of the child, fever, anemia of the mother, body mass index of the mother, mother’s education level, mother’s knowledge on nutrition, age of household head, source of drinking water, toilet facilities, place of residence of household, source of drinking water and province were found to be significantly related to poverty and malnutrition. The study revealed a positive correlation between poverty of household and malnutrition of children less than five year

Prevalence and Risk Factors Associated with Anemia among Women of Childbearing Age in Rwanda

Anemia among women of child bearing age is a global public health problem. In developing countries such as Rwanda, women and their children may be particularly susceptible to anemia. The main objectives of this study were to assess the prevalence of anemia among women of reproductive age in Rwanda and to identify the risk factors associated therewith. The current study considered socio-economic, demographic and environmental factors and the 2014/2015 Rwanda Demographic and Health Survey data was used for this purpose. Due to the complexity of the sampling design, the present study used survey logistic model that takes account of sampling weight, stratification and clustering. The SAS statistical software was used for the analysis of the results. The anemia status was assessed among 6 680 women aged between 15 and 49 years old and the prevalence of anemia among women of this child bearing age group, was found to be 19.2%. The study also revealed that body mass index, contraceptive use, use of mosquito bed nets, marital status, wealth quintile of the household, size of the household, literacy, tobacco use, type of cooking fuel, type of toilet facilities, type of source of drinkable water, and province of residence, were all factors associated with anemia among women of reproductive age in Rwanda. Hence the current study highlights several health, geographical and socio-economic issues that can assist health care professionals and other relevant authorities in fostering an environment that reduces the risk of anemia for women and children. Keywords: Anemia, women, survey logistic, Rwanda, RDHS 2014/15 L'anémie chez les femmes en âge de procréer est un problème de santé publique mondial. Dans les pays en développement comme le Rwanda, les femmes et leurs enfants peuvent être particulièrement sensibles à l'anémie. Les principaux objectifs de cette étude étaient d'évaluer la prévalence de l'anémie chez les femmes en âge de procréer au Rwanda et d'identifier les facteurs de risque qui y sont associés. La présente étude a pris en compte les facteurs socio-économiques, démographiques et environnementaux et les données de l'enquête démographique et sanitaire du Rwanda 2014/2015 ont été utilisées à cette fin. En raison de la complexité du plan d'échantillonnage, la présente étude a utilisé un modèle logistique d'enquête qui tient compte du poids d'échantillonnage, de la stratification et du regroupement. Le logiciel statistique SAS a été utilisé pour l'analyse des résultats. Le statut anémique a été évalué chez 6 680 femmes âgées de 15 à 49 ans et la prévalence de l'anémie chez les femmesde ce groupe d'âge en âge de procréer s'est avérée être de 19,2%. L'étude a également révélé que l'indice de masse corporelle, l'utilisation de contraceptifs, l'utilisation de moustiquaires, l'état matrimonial, le quintile de richesse du ménage, la taille du ménage, l'alphabétisation, l'usage du tabac, le type de combustible de cuisson, le type de toilettes, le type de source d'eau potable et la province de résidence, étaient tous des facteurs associés à l'anémie chez les femmes en âge de procréer au Rwanda. Par conséquent, la présente étude met en évidence plusieurs problèmes de santé, géographiques et socio-économiques qui peuvent aider les professionnels de la santé et d'autres autorités compétentes à favoriser un environnement qui réduit le risque d'anémie pour les femmes et les enfants. Mots-clés: Anémie, femmes, logistique d'enquête, Rwanda, RDHS 2014/1

Determinants of Domestic Violence in Women of Reproductive Age in Rwanda

Domestic violence is a global public health problem. It is prevalent in both the developed world and developing countries. The objective of this study is to identify the factors that are associated with domestic violence against women of reproductive age in Rwanda. The data from the 2014/2015 Rwanda demographic and health survey were used. Generalized linear mixed model was used to account for random effects, overdispersion of residual and heterogeneity. The findings of this study revealed that wealth quintiles, education level of the husband or partner, polygamy, alcohol status of husband or partner, size of the family, number of sexual partners including the husband in the last 12 months, the province the victim lived in, the ownership of an asset in the form of a house or land and the societal attitude towards wife-beating, were the determinants of domestic violence in women of reproductive age. The findings of the risk factors in the current study can help the policy makers, public health workers and institutions in charge of gender monitoring in Rwanda to come up with effective strategies to reduce the domestic violence levels directed against women.&nbsp

Indirect child mortality estimation technique to identify trends of under-five mortality in Ethiopia

Background: In sub-Saharan African countries, the chance of a child dying before the age of five years is high. The problem is similar in Ethiopia, but it shows a decrease over years.Methods: The 2000; 2005 and 2011 Ethiopian Demographic and Health Survey results were used for this work. The purpose of the study is to detect the pattern of under-five child mortality overtime. Indirect child mortality estimation technique is adapted to examine the under-five child mortality trend in Ethiopia.Results: From the result, it was possible to see the trend of under-five child mortality in Ethiopia. The under-five child mortality shows a decline in Ethiopia.Conclusion: From the study, it can be seen that there is a positive correlation between mother and child survival which is almost certain in any population. Therefore, this study shows the trend of under-five mortality in Ethiopia and decline over time.Keywords: EDHS, under-five mortality, parity, indirect technique, CEB, children survivin

A regression analysis of discrete time competing risks data using a vertical model approach

Over the years, the standard regression analysis method for discrete time competing risks data has been to model the data with discrete time cause-specific hazards. While a few continuous time competing risks models have been proposed in the literature, it is a well documented fact that these models are not appropriate for application in discrete time as is. The vertical regression model of Nicolaie et al. (2010) is the latest of these continuous time competing risks models. We reformulate this regression model for the purpose of application in discrete time. We demonstrate that the proposed model can easily be implemented by using existing software for discrete time models. We apply the proposed model together with some of the existing discrete time models to real discrete time competing risks data and find that the proposed model and these models compare favourably

The level of difficulty and discrimination power of the items of the National Senior Certificate Mathematics Examination

South Africa’s National Senior Certificate examination system was introduced in 2008 as a single national examination system, in order to facilitate fair and standardised assessment and to provide all learners with an equal chance of access to higher education. However, limited research has been done to investigate the discrimination power of the actual examination items and the spread difficulty level for learners from different school quintile types. The purpose of the study reported on here was to investigate differential performance of learners in the items of the 2009 National Senior Certificate mathematics examination. The dataset used in this study was from the Western Cape (WC) Education Department. From the analysis, the results show that the discrimination power of the different examination questions was not identical across different school quintiles. Further investigation of the data reflects a considerable range of category difficulty levels, with higher (above average) ability levels being tested for learners in the quintile 1 to quintile 4 schools, while only learners with average abilities were being tested in the quintile 5 and independent schools