Delia North

University of KwaZulu-Natal | ukzn · School of Mathematics, Statistics and Computer Science

Background Air pollution and several prenatal factors, such as socio-demographic, behavioural, physical activity and clinical factors influence adverse birth outcomes. The study aimed to investigate the impact of ambient air pollution exposure during pregnancy adjusting prenatal risk factors on adverse birth outcomes among pregnant women in MACE bi...

Teacher well-being is an important issue that needs to be considered within a teaching environment. However, little research exists about the relationship between teacher well-being and learner performance. In this study we used data from the 2015 Trends in International Mathematics and Science Study (TIMSS) to look at the interplay between teacher...

The purpose of this study is to explore the expressions of confidence by a group of South African mathematics teachers about teaching mathematics and statistics concepts from various perspectives. The participants were 75 mathematics teachers who were teaching Grades 4 to 12 in KwaZulu-Natal (KZN) schools. They then were asked to express their opin...

Household food insecurity remains highly prevalent in developing countries (including in Ethiopia) and it has been recognized as a serious public health problem. Several factors such as demographic, economic, social, and clinical factors influence household food insecurity, and these vary geographically. In this work, we investigate the geographica...

Unsuppressed HIV viral load is an important marker of sustained HIV transmission. We investigated the prevalence, predictors, and high-risk areas of unsuppressed HIV viral load among HIV-positive men and women. Unsuppressed HIV viral load was defined as viral load of ≥400 copies/mL. Data from the HIV Incidence District Surveillance System (HIPSS),...

Unmeasured confounding can cause considerable problems for causal inference in observational studies and threaten the validity of the estimates of causal treatment effects. We investigate the robustness of a relatively new causal inference technique, targeted maximum likelihood estimation (TMLE), in terms of its robustness against the impact of unm...

New HIV infections among young women remains exceptionally high and to prevent onward transmission, UNAIDS set ambitious treatment targets. This study aimed to determine the prevalence, spatial variation and factors associated with unsuppressed HIV viral load at ≥400 copies per mL. This study analysed data from women aged 15–49 years from the HIV I...

Background Sustainable Human Immunodeficiency Virus (HIV) virological suppression is crucial to achieving the Joint United Nations Programme of HIV/AIDS (UNAIDS) 95–95-95 treatment targets to reduce the risk of onward HIV transmission. Exploratory data analysis is an integral part of statistical analysis which aids variable selection from complex s...

Selection bias is a fundamental reason why the estimation of treatment effects in observational studies is not as straightforward as in well-designed experiments. We introduce an improved and generalized matching method based on redefining how the Mahalanobis distance can be used for matching to reduce covariate imbalance and improve the efficiency...

Recent studies have expanded the focus of machine learning methods like random forests beyond prediction. They have found utility in the area of causal inference by using it to estimate propensity scores. It has also been established in the literature that tuning the hyperparameter values of random forests can improve the estimates of causal treatm...

Background Epidemiological theory and many empirical studies support the hypothesis that there is a protective effect of male circumcision against some sexually transmitted infections (STIs). However, there is a paucity of randomized control trials (RCTs) to test this hypothesis in the South African population. Due to the infeasibility of conductin...

We present entropy balancing – a relatively new technique for estimating treatment effects, which has been under-utilised in the applied biomedical literature. Our objective is to share our experiences learned from using entropy balancing in nonexperimental studies, via Monte Carlo simulations and two empirical examples. We used the inverse probabi...

Background: Birth weight, birth length, and gestational age are major indicators of newborn health. Several prenatal exposure factors influence the fetal environment. The aim of the study was to investigate the effect of prenatal exposure factors, including socio-demographic, behavioural, dietary, physical activity, clinical and environmental on b...

Predicting the number of total children ever born in a country is a key component for proper implementation of economic growth policy. Here, performance metrics were used to predict models that appropriately describe the factors that affect children ever born. A comparison of 60% training and 40% validation, 70% training and 30% validation, 80% tra...

Introduction Epidemiological theory and many empirical studies support the hypothesis that there is a protective effect of medical male circumcision (MMC) against HIV infection. We aim to test this claim with evidence from a high endemic community in South Africa. Methodology We analysed a cross-sectional dataset, including HIV test outcome and MM...

Log linear hedonic models are ubiquitous in econometric real estate research even though functional form assumptions are often not satisfied and the nested structure of homes in suburbs is not captured adequately. This study focuses on appraising different residential property types located throughout South Africa, investigating a flexible approach...

Unmeasured confounding can cause considerable problems in observational studies and may threaten the validity of the estimates of causal treatment effects. There has been discussion on the amount of bias in treatment effect estimates that can occur due to unmeasured confounding. We investigate the robustness of a relatively new causal inference tec...

Background Sub-Saharan Africa, as opposed to other regions, has the highest under-five mortality rates yet makes the least improvement in reducing under-five mortality. Despite the decline, Ethiopia is among the top ten countries contributing the most to global under-five mortalities. This article examines the impact of the number of antenatal care...

Background: Epidemiological theory and many empirical studies support the hypothesis that there is a protective effect of male circumcision against some sexually transmitted infections (STIs). However, there is a paucity of randomized control trials (RCTs) to test this hypothesis in the South African population. Due to the infeasibility of conducti...

The South African education system bears evidence of fluctuations in the final Grade 12 mathematics marks occurring across different learner profiles. This study reflected on the National Senior Certificate (NSC) mathematics results from the Western Cape Education Department for the years 2009 to 2014, the period just after the introduction of the...

The rapid increase in total children ever born without a proportionate growth in the Nigerian economy has been a major concern. The total children ever born, being a count data, requires applying an appropriate regression model. Poisson distribution is the ideal distribution to describe this data, but it is deficient due to equality of variance and...

Background: HIV infected patients may experience many intermediate events including between-event transition throughout their follow up. Through modelling these transitions, we can gain a deeper understanding of HIV disease process and progression and of factors that influence the disease process and progression pathway. In this work, we present t...

Background: Ordinal health longitudinal response variables have distributions that make them unsuitable for many popular statistical models that assume normality. We present a multilevel growth model that may be more suitable for medical ordinal longitudinal outcomes than are statistical models that assume normality and continuous measurements. M...

Background: Maternal dietary habits during pregnancy are considered essential for development and growth of the fetus as well as maternal health. It has an effect on the birthweight of infants. However, little is known about the effect of dietary patterns on birthweight in urban South Africa. This study aimed to investigate differential effect of...

We propose that a parallel coordinates plot can be used to study multidimensional data particularly to explore discovery of patterns across the variables. This can assist researchers from the health sciences to visualize their cohort data with interactive data analysis. The study used data from Mother and Child in the Environment birth cohort in Du...

Introduction: Combination antiretroviral therapy has become the standard care of human immunodeficiency virus (HIV) infected patients and has further led to a dramatically decreased progression probability to acquired immune deficiency syndrome (AIDS) for patients under such a therapy. However, responses of the patients to this therapy have recorde...

Background This article examines the impact of antenatal care on child health outcome. We specifically investigated if women visits to antenatal care services has a positive effect in the reduction of under-five mortality. Methods We employ a difference-in-differences design with propensity score matching to identify direct causal effects of antena...

Background: CD4 cell and viral load count are highly correlated surrogate markers of human immunodeficiency virus (HIV) disease progression. In modelling the progression of HIV, previous studies mostly dealt with either CD4 cell counts or viral load alone. In this work, both biomarkers are in included one model, in order to study possible factors...

Preterm birth is a common cause of death worldwide of children under the age of five years. This condition is linked with short and long term neonatal morbidity and mortality. Maternal nutrition during pregnancy has a profound effect on fetal growth and development and subsequently also on the incidence of preterm birth. The aim of this study was t...

Background: Patients infected with HIV may experience a succession of clinical stages before the disease diagnosis and their health status may be followed-up by tracking disease biomarkers. In this study, we present a joint multistate model for predicting the clinical progression of HIV infection which takes into account the viral load and CD4 cou...

Background: Longitudinal quality of life (QoL) is an important outcome in many chronic illness studies aiming to evaluate the efficiency of care both at the patient and health system level. Although many QoL studies involve multiple correlated hierarchical outcome measures, very few of them use multivariate modeling. In this work, we modeled the l...

In response to invasion by the human immunodeficiency virus (HIV), the self-regulatory immune system attempts to restore the CD4+ count fluctuations. Consequently, many clinical covariates are bound to adapt too, but little is known about their corresponding new optimal set points. It has been reported that there exist few strongest clinical covari...

Birthweight is strongly associated with infant mortality and is a major determinant of infant survival. Several factors such as maternal, environmental, clinical, and social factors influence birthweight, and these vary geographically, including across low, middle, and economically advanced countries. The aim of the study was to investigate the geo...

Due to the heterogeneous nature of residential properties, determining selling prices which will reconcile supply and demand is difficult. Establishing realistic listing prices is vitally important for sellers to prevent prolonged time on market. Sellers have several resources available to assist in this endeavour, all of which involve understandin...

Orientation: Residential property markets play an important role in economies, informing policy development and decision-making. However, measuring quality-adjusted growth is difficult because of the heterogeneity of properties. Hedonic regression is frequently used in real estate econometric studies as a quality-adjusted technique to estimate resi...

This work is copyrighted by Università del Salento, and is licensed under a Creative Commons Attribuzione-Non commerciale-Non opere derivate 3.0 Italia License. For more information see: http://creativecommons.org/licenses/by-nc-nd/3.0/it/ In observational studies, propensity score weighting methods are regarded as the conventional standard for est...

Purpose: To investigate the variation in CD4 count between HIV positive patients due to clinical covariates at each phase of the HIV disease progression. Patients and methods: The Centre for the AIDS Programme of Research in South Africa (CAPRISA) conducted different studies in which female patients were initially enrolled in HIV negative cohorts (...

Propensity score methods have dominated the estimation of treatment effects based on observational data and particularly in the health and medical sciences. We propose a weighting method based on rank-based Mahalanobis distance, namely the covariate balancing rank-based Mahalanobis distance method, to estimate causal effects for observational data....

Introduction Past endeavours to deal with the obstacle of expensive Cluster of Difference 4 (CD4⁺) count diagnostics in resource-limited settings have left a long trail of suggested continuous CD4⁺ count clinical covariates that turned out to be a potentially important integral part of the human immunodeficiency virus (HIV) treatment process during...

It is often claimed that technology can be used as a tool that can facilitate teaching and learning and contribute to learners’ achievement. This article reports on a study about how KwaZulu-Natal mathematics teachers use, access and integrate technology in the teaching and learning of mathematics. A questionnaire containing closed and Likert scale...

The purpose of this paper is to examine South African teachers' suggestions for improving the teaching and learning of mathematics and statistics, as well as exploring relationships between certain demographic factors and the number and types of strategies suggested by teachers. The study was conducted with 75 South African mathematics teachers. We...

Three properties of dissolving pulp namely lignin, viscosity and the α-cellulose were investigated. A laboratory experiment for the dissolving wood pulping process was conducted on nine Eucalyptus genotypes: Edunnii, Esmithii, Egrandis, Macarthurii, Emearnsii, Enitens, GCG438, GUA380 and GUW962. Repeated measurements were taken at each of the six p...

Paying attention to the planning of lessons represents a crucial teaching task. This paper analyses teachers' framing of lesson objectives and their descriptions of how they would introduce particular mathematics topics. Connections between the objectives and the instructional strategies employed, were also studied. The study involved 75 South Afri...

What teachers teach, how they teach it and when they teach it should be guided by the curriculum. This paper focuses on teachers’ reports about how they integrate the curriculum documentation in teaching mathematics and statistics concepts. Questionnaires containing both Likert scale and closed and open-ended questions were administered to 75 mathe...

Methods: Multiple imputation and subset correspondence analysis are applied to a set of child asthma data that is mainly categorical and suffers from non-response. Differences in the methods and in the outcomes they produce are studied. In addition, the inclusion of interactions in a subset correspondence analysis is illustrated. Results: Despite t...

In this paper, we propose a new approach to extreme value modelling for the forecasting of Value-at-Risk (VaR). In particular, the block maxima and the peaks-over-threshold methods are generalised to exchangeable random sequences. This caters for the dependencies, such as serial autocorrelation, of financial returns observed empirically. In additio...

Teaching approaches and assessment practices are key factors that contribute to the improvement of learner outcomes. The study on which this article is based, explored the methods used by KwaZulu-Natal (KZN) teachers in teaching and assessing mathematics and statistics. An instrument containing closed and open-ended questions was distributed to sev...

Extreme value theory (EVT) is commonly used for evaluating risk in financial returns. In particular, it can be amalgamated with a GARCH model, where the peaks-over-threshold (POT) method is applied to the innovations. However, this GARCH-EVT approach relies on the assumption that the innovations are independent and identically distributed. To relax...

In estimating the population mean of a study variable y, we can often use a ratio-type estimator when a related auxiliary variable x, with improved accessibility, is available. In cases where x is qualitative, or may be categorised, and a double sampling plan is used, we may consider a two-phase stratified sampling design. Traditionally, it is assu...

The application of subset correspondence analysis is a relatively new technique to deal with the analysis of categorical data with missingness. A simulation study is used to test the effects of Little and Rubin's missingness mechanisms, as well as missingness up to 50% on subset correspondence analysis. Missingness was simulated across 18 different...

South African municipalities are faced with the challenges of growing demand for services. This study models the energy consumption estimation practice within the Durban municipal area. It was found that an estimation technique that accounts for the seasonal and monthly effects, as well as residential type, predicts monthly individual household ele...

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...

In the presence of linear trend, linear systematic sampling (LSS) is less efficient than stratified random sampling (STR) and more efficient than simple random sampling (SRS). Consequently, some authors have proposed modifications to the LSS design, which have shown to yield optimal results under certain conditions. In this paper, a further modifie...

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...

In this paper, we propose a sampling design termed as multiple-start balanced modified systematic sampling (MBMSS), which involves the supplementation of two or more balanced modified systematic samples, thus permitting us to obtain an unbiased estimate of the associated sampling variance. There are five cases for this design and in the presence of...