Research Articles (Statistics)
Permanent URI for this collectionhttp://hdl.handle.net/2263/1835
A collection containing some of the full text
peer-reviewed/
refereed articles published by researchers from
the
Department
of Statistics
Browse
Recent Submissions
Now showing 1 - 20 of 538
Item Self-perception and clinical presentation of eating and swallowing difficulties within elderly care(AOSIS, 2025-03) Bell, Caitlin Shauna; Kruger, Esedra; Vermeulen, Rouxjeanne; Masenge, Andries; Pillay, Bhavani S.; bhavani.pillay@up.ac.zaBACKGROUND : The growing ageing population requires effective management of complex medical diagnoses and healthy ageing support within residential care facilities. However, limited access to guidelines on monitoring residents’ eating and swallowing abilities has been reported. Recent research is critical for future policy development. OBJECTIVES : This study aimed to compare self-perceived and clinical presentation of eating and swallowing abilities among a portion of elderly residents to enhance management of the residential care population within the South African context. METHOD : This comparative, within-subject research study assessed 44 participants using an oropharyngeal dysphagia protocol including a medical history review, the Eating Assessment Tool – 10 (EAT-10), the Mann Assessment of Swallowing Abilities (MASA), and the three-ounce water test of the Yale Swallow Protocol (YSP). A brief cognitive screener was used when cognitive impairment was unknown. RESULTS : Of the participants, 21 out of 44 (48%) self-reported concerns for oropharyngeal dysphagia. Evidence of compensatory eating behaviours, without therapeutic intervention, was found. A negative, low correlation was present between the EAT-10 and the MASA (r = -0.306, p < 0.05) scores. CONCLUSION : Individuals who self-reported eating and swallowing difficulties demonstrated fewer clinical symptoms, potentially due to compensatory techniques. The disparity between patient-reported outcome measures and clinical assessment tools highlights the need for robust screening and assessment policies within this context. CONTRIBUTION : This study highlights the importance of holistic assessment practices by integrating self-perception with clinical findings to address oropharyngeal dysphagia incidence within this complex population.Item Newborn birth weight and its associated risk factors in Somalia using Somalia health and demographic survey(Elsevier, 2025-03) Belay, Denekew Bitew; Birhan, Nigussie Adam; Ali, Mahad Ibrahim; Chen, Ding-Geng (Din)Please read abstract in the article.Item Rejoinder to the ‘Letter to the Editor’ on “Group-by-treatment interaction effects in comparative bioavailability studies”(Springer, 2025-02) Schütz, Helmut; Burger, Divan Aristo.; Cobo, Erik; Dubins, David; Farkas, Tibor; Labes, Detlew; Lang, Benjamin; Ocana, Jordi; Ring, Arne; Shitova, Anastasia; Stus, Volodymyr; Tomashevskiy, MichaelNo abstract available.Item Bayesian nonparametric estimation of differential entropy for toroidal data(Elsevier, 2025-12) Rad, Najmeh Nakhaei; Arashi, Mohammad; Bekker, Andriette, 1958-; Millard, Sollie M.; najmeh.nakhaeirad@up.ac.zaEntropy is a widely used information-theoretic measure; however, the estimation of entropy for observations of a periodic nature has not received much attention thus far. In this paper, we implement a Bayesian approach to obtain nonparametric estimates of Shannon entropy for toroidal data. This paves the way for its use in protein structure validation through an approach based on information theory and the distribution of backbone dihedral angles in the 3D structure of proteins. In addition, the kernel density estimation proposed in this paper can be applied alongside available parametric models for modeling toroidal observations. Simulation studies and the analysis of real datasets provide insights into this proposed method for protein structure validation. HIGHLIGHTS • Estimation of entropy for observations of a periodic nature specifically toroidal data. • A Bayesian nonparametric density estimator for toroidal data using a Dirichlet infinite mixture model. • Considering the possible dependencies between two circular variables. • An alternative information-theory based method for protein structure validation. • Diagnosing of the disordered pattern of wind direction in univariate case.Item A refreshing take on the inverted Dirichlet via a mode parameterization with some statistical illustrations(Springer, 2025-03) Otto, Arno F.; Ferreira, Johannes Theodorus; Bekker, Andriette, 1958-; Punzo, A.; Tomarchio, S.D.; arno.otto@up.ac.zaThe inverted Dirichlet (IDir) distribution is a popular choice for modeling multivariate data with positive support; however, its conventional parameterization can be challenging to interpret. In this paper, we propose a refreshing take on the IDir distribution through a convenient mode-based parameterization, resulting in the mode-reparameterized IDir (mIDir). This new parameterization aims to enhance the use of the IDir in various contexts. We provide relevant statistical illustrations in robust and nonparametric statistics, model-based clustering, and semiparametric density estimation, all benefiting from this novel perspective on the IDir for computation and implementation. First, we define finite mIDir mixtures for clustering and semiparametric density estimation. Secondly, we introduce a smoother based on mIDir kernels, which, by design, avoids allocating probability mass to unrealistic negative values, thereby addressing the boundary bias issue. Thirdly, we introduce a heavy-tailed generalization of the mIDir distribution, referred to as the contaminated mIDir (cmIDir), which effectively handles and detects mild outliers, making it suitable for robust statistics. Maximum likelihood estimates of the parameters for the parametric models are obtained using a developed EM algorithm as well as direct numerical optimization. A parameter recovery analysis demonstrates the successful application of the estimation method, while a sensitivity analysis examines the impact of mild outliers on both the mIDir and cmIDir models. The flexibility and advantages of the proposed mIDir-based models are showcased through several real data analyses and illustrations.Item Spatiotemporal models with confounding effects : application on under-five mortality across four sub-Saharan African countries(Frontiers Media, 2025-01) Fenta, Haile Mekonnen; Chen, Ding-Geng (Din); Zewotir, Temesgen T.; Rad, Najmeh NakhaeiBACKGROUND : Different strategies have been developed to minimize under-five mortality (U5M) in sub-Saharan African (sSA) countries; however, it is still a major health concern for children in the region. Spatiotemporal modeling is important for areal data collected over time. However, when the number of time points and spatial areas is large and the areas are disconnected, fitting the model becomes computationally complex because of the high number of required parameters to be estimated. Therefore, the main aim of this study is to adopt a spatiotemporal dynamic model that includes the confounding effects between time, space, and their interactions with fixed covariates, with a special emphasis on U5M across disconnected sSA countries. METHOD : We used nationally publicly representative Demographic and Health Survey (DHS) data for the period from 2000 to 2020. Bayesian spatiotemporal hierarchical modeling with an integrated nested Laplace approximation (INLA) program was used to model the spatiotemporal distribution of U5M among children across 37 districts located in four disconnected sSA regions: Ethiopia, Nigeria, Zimbabwe, and Ghana. RESULTS : A total of 170,356 under-five children from 37 districts were considered, and 15,467 died before the age of five. The relative risk of U5M in the first DHS was 2.02, which sharply decreased to 0.5 in the recent phase. The proportion of improved access to water, sanitation, clean fuel use, urbanization, and access to health facilities in the district had a significant negative association with U5M. The higher the proportion of these covariates, the lower is the prevalence of childhood mortality. CONCLUSION : This study revealed evidence of strong spatial, temporal, and interaction effects that influence under-five mortality risk across districts. Improving the women’s literacy index, access to improved water, the use of clean fuel, and the wealth index are associated with an improvement in the risk of mortality among under-five children across the districts. Districts in Nigeria and Ethiopia have the highest risk of U5M; hence, districts in these countries require special attention.Item Determinants of community-acquired pneumonia among under-five children in Awi Zone, Northwest Ethiopia(Frontiers Media, 2025-05) Birhan, Nigussie Adam; Workineh, Alene Yirsaw; Wolde, Zelalem Meraf; Abich, Emebiet; Alemayehu, Gedif Mulat; Nigussie, Atalaye; Alemu, Yenew; Messfin, Chalachew Alemi; Belay, Denekew BitewBACKGROUND : Globally, community-acquired pneumonia is the leading cause of death in under-five children, accounting for 7.6 million deaths. Among these deaths, approximately 99% occur in low and middle-income countries. The present study aimed to assess the magnitude of community-acquired pneumonia and its associated factors among under-five children in Awi Zone. METHODS : A community cross-sectional study was conducted on 1,368 participants from March to July 2023. A multistage sampling method was used. Data were entered into Epi-Data and exported to STATA for analysis. Bivariable and multivariable logistic regressions were used. Variables with a p-value of < 0.05 were considered statistically significant. RESULTS : The percentage of community-acquired pneumonia among under-five children was 11.33% (95% CI: 9.75-13.12%). Primary education [AOR = 0.38; 95% CI:0.15, 0.95], stunting [AOR = 4.80; 95% CI: 2.31, 9.94], diarrhea [AOR = 3.75; 95% CI: 1.96, 7.18], acute lower respiratory tract infection [AOR = 14.57, 95% CI: 3.18, 66.78], acute upper respiratory tract infection [AOR = 9.06; 95% CI: 2.03, 40.42], and presence of separate kitchen [AOR = 0.38, 95% CI: 0.20, 0.72] were associated with community-acquired pneumonia. CONCLUSION : In this study, the percentage of community-acquired pneumonia was relatively high. Hence, we recommend adequate health education in areas such as nutritional intervention, the prevention and early treatment of diarrhea and acute respiratory tract infections (ARTI), and preventing indoor air pollution to reduce the risk of community-acquired pneumonia.Item Determinants of child malnutrition and morbidity in Ethiopia : a structural equation modeling approach(Frontiers Media, 2025-04) Warssamo, Birhanu Betela; Belay, Denekew Bitew; Chen, Ding-Geng (Din)BACKGROUND : Childhood malnutrition and morbidity remain significant public health challenges in Ethiopia, highlighting the need to assess the risk factors contributing to these issues for effective prevention and control strategies. Thus, this study aims to investigate the underlying risk factors by employing a structural equation model to analyze malnutrition as a mediator in the relationship between selected factors and morbidity. METHODS : The study utilized data from the 2016 Ethiopia Demographic and Health Survey and a sample of 8,560 under-five children were considered. The structural equation model was used to examine the association between child malnutrition, morbidity, and potential risk factors. The structural equation model makes it possible to analyze malnutrition as a mediator of the association between selected risk factors and morbidity. RESULTS : Out of the 8,560 sampled children, 12.80% were wasted, 34.75% were stunted, 23.91% were underweight, 13.9% had fever, 11.2% had diarrhea, and 59.7% had anemia. Birth interval, wealth index household, place of delivery, size of child at birth, number of children, and socioeconomic condition had a significant direct effect on childhood malnutrition and morbidity. The time to get water, toilet facility, and child is a twin variables had direct effects on childhood malnutrition and had no significant direct effects on childhood morbidity. Time to get water, birth interval, toilet facility, wealth index of household, child is a twin, place of delivery, size of child, and number of children exhibited an indirect effect on morbidity through malnutrition. CONCLUSIONS : The study revealed that there was a high prevalence of malnutrition and morbidity among under-five children in Ethiopia. Time to get water in min, place of delivery, size of child, and number of children showed a significant indirect and total effect on morbidity through malnutrition and socioeconomic conditions showed a significant total effect on morbidity via malnutrition. Implementing and extending programs such as community-based nutrition interventions for early childhood is critical, as early malnutrition showed long-term effects on growth and immunity, particularly in the regions of Affar, Dire Dawa, Gambela, Harari, Amhara, and Somali.Item Exploring the impact of a maternal support grant to improve mental health and food security amongst pregnant women in South Africa during the COVID-19 pandemic(Wiley, 2024-09) Laurenzi, Christina A.; Menyatsoe, Masedi; Shuaib, Mustafa; Edwards, Amanda; Gemmell, Kelly; Geffen, Hayli; Tomlinson, Mark; Muller, Anna‐Marie; Manda, S.O.M. (Samuel); Mabaso, Kopano M.Social protection during pregnancy may support pregnant women struggling to meet basic needs to ensure a healthy pregnancy and buffer negative impacts of multiple adversities. We assessed the effect of a bimonthly digital food voucher, delivered to pregnant women during the COVID-19 pandemic in the Cape Town area, on their mental health, hunger, and dietary diversity. Pregnant women from antenatal clinics in specific high-poverty areas were invited to join the voucher program; a subset was recruited for in-depth telephone interviews. Interviews were conducted before, during, and after voucher distribution. Generalized estimating equations were fit to examine whether each outcome was associated with voucher exposure over time. Of the 205 participants, most were aged 25–34, not recently employed, with at least one child in their household. Approximately 1/3 were first-time mothers and 32% reported mental health difficulties. Voucher exposure over 12 months was associated with significant reductions in mental health symptoms at midline and endline. Maternal hunger was reduced at midline and endline. High mental health scores were significantly associated with increased maternal hunger after adjusting for potential confounders. This study provides preliminary evidence for income support during pregnancy to shape positive health outcomes in South Africa.Item Generalized bivariate Kummer-beta distribution with marginals defined on the unit interval(Public Library of Science, 2024-10-28) Shabgard, Sina; IranmaneshID, Anis; Rad, Najmeh Nakhaei; Nagar, Daya K.; Nadarajah, SaraleesIn this paper, a generalized bivariate Kummer-beta distribution is proposed. The name derives from the fact that its particular cases include univariate Kummer-beta distributions. This distribution generalizes a number of existing bivariate beta distributions, including Nadarajah’s bivariate distributions, Libby and Novick’s bivariate beta distribution and a central bivariate Kummer-beta distribution. Various properties associated with this newly introduced distribution are derived. The derived properties include product moments, marginal densities, marginal moments, conditional densities, conditional moments, Rényi entropy and Shannon entropy. Motivated by possible applications in economics, genetics, hydrology, meteorology, nuclear physics, and reliability, we also derive distributions of the product and the ratio of the components following the proposed distribution. Parameter estimation by maximum likelihood method is discussed by deriving expressions for score functions. Inference based on maximum likelihood estimation supposes that the maximum likelihood estimators have zero bias and zero mean squared errors. A simulation study is performed to check this for finite samples.Item Additive modeling of zonal level crop production in Ethiopia(Nature Research, 2025-04) Mare, Yidnekachew; Zewotir, Temesgen; Belay, Denekew BitewCrop production is the main source of food security and income for smallholder private farmers in Sub-Saharan countries. To have a sustainable source of food security and economy, it is important to identify covariates that affect crop production linearly and nonlinearly. Annual agricultural sample survey data of eight Meher seasons, from 2012/13 to 2019/20, is used in this study with the main objective of identifying the set of covariates that have linear and nonlinear effects on crop production and estimating their effects using an additive mixed effects model. The minimum, mean, and maximum crop production across the country for the study period were 1.616, 8.693, and 147.843 quintals, respectively, and 50% of the farmers produced less than 6.95 quintals. The histogram, kernel density, and P-P plots suggested that log-transformed crop production is approximately normally distributed. From the competing models’ summary statistics, information criteria values, and analysis of variance tests, relaxing the linearity assumption and including a random effect in the model has improved model performance, suggesting the additive mixed effects model best fits the data on hand. Gambella, SNNP, and Oromia regions have significantly different overall mean crop production than the reference in Dire Dawa town. Covariates like year, proportion of female farmers, household age, and UREA fertilizer used have a significant nonlinear effect, while covariates like proportion of educated farmers, area used, and proportion of farmers who received credit service have a significant linear effect on log crop production. The basic model assumptions are not violated, so the final additive mixed effects model can be used for prediction and inference purposes. We recommend farmers use more croplands, indigenous seeds, and UREA fertilizer; practice pure agriculture; and participate in local farmers associations. Policies regarding the participation of female and educated farmers, the implementation and effectiveness of credit services and extension programs, private investors to participate in crop production, and the provision of farm inputs to the elderly farmers should be revised.Item Behaviour of commercial layer hens in enriched cages and floor systems examined using human and video-based observations(South African Society for Animal Science, 2025-06) Chilemba, Timothy.; Van Marle-Koster, Este; Masenge, Andries; Cromhout, M.; Nkukwana, Thobela T.; evm.koster@up.ac.zaThere is considerable pressure to eliminate the use of conventional cages in commercial layer hen production systems. However, the assessment of alternative systems that can ensure the hen's ability to perform natural behaviours, while simultaneously enhancing farm productivity and economic efficiency, remains incomplete. This study assessed layer behaviour in a floor system and in enriched cages on a commercial layer farm using human and video-based observations. The study focused on dust bathing, nesting, feather pecking, and perching behaviours, and on the formation of mud balls on the feet. A large proportion (72.9%) of the hens exhibited dust-bathing behaviour, with an average duration of 22.63 minutes. Feather pecking was exhibited by 35.4% of layers in the enriched cages, compared to 58.3% of layers in the floor system. Overall, feather pecking was the least observed behaviour. Layers in enriched cages used perches more (47%) than layers in the floor system (27%), and a negative association was found between body weight and perching in layers in the floor system. At the end of the six-week trial period, 41.67% of the hens had developed mud balls on their toes that exceeded 3 cm in length. The results of this study provide evidence of the relationships between poultry behaviour, welfare, and production. Video-based observations confirmed that farm managers may not be able to identify certain welfare-related behavioural aspects unless they are closely monitored. The results of this study may be used to inform stakeholders about behaviour and welfare considerations in the management of commercial layers.Item Identifying the associated risk factors of time to first antenatal care contacts among pregnant women in Somalia : a survival frailty approach(Bentham Science Publishers, 2025-01) Belay, Denekew Bitew; Fentaw, Kenaw Derebe; Ali, Mahad Ibrahim; Rad, Najmeh Nakhaei; Chen, Ding-Geng (Din)BACKGROUND : Antenatal care (ANC) utilization offers a wide range of interventions, such as education, counseling, screening, treatment, monitoring, and supporting the health of pregnant women, making it a significant opportunity for expectant mothers. This study aims to investigate the time to the first ANC contact among pregnant women and to identify associated factors by employing the Accelerated Failure Time (AFT) model using different frailty distributions. METHODS : This study used Somalia's Health and demographic survey data. A sample of 3138 women of reproductive age (15-49 years) were included in the study and accelerated failure time (AFT) models with different frailty distributions were compared using information criteria to select the best model. RESULTS : Among the women included in this study, only 33.1% of them received their first ANC contacts within the recommended time during their pregnancy. A gamma frailty model with log-logistic as base-line distribution was found to be the best model for the time-to-first ANC utilization for our data. The final model, based on the log-logistic gamma frailty, identified marital status, mother's occupation, wanted pregnancy, region, parity, wealth index, education level of mother, persons deciding on mother health care, and media exposure are significant (p-value <0.05) predictors of time to the first ANC contact in Somalia. The final model evidenced a high degree of heterogeneity at an individual level regarding the time to the first ANC utilization in Somalia. CONCLUSION : The median time for the first ANC contact among pregnant women was 6.2 months. To ensure accurate analysis and better policy recommendation, different candidate models were compared, and the univariate gamma frailty model with a log-logistic baseline was found to be the most appropriate approach for analyzing time to the first ANC contact among pregnant women. Maternal and child health policies and initiatives must better focus on women's development and implement interventions aimed at increasing the timely initiation of prenatal care services. More specific policy measures, such as targeted educational campaigns, improved pregnancy services, and efforts to minimize regional disparities, should be prioritized as urgent intervention mechanisms.Item Meta-analysis of the prevalence of tuberculosis in cattle and zoonotic tuberculosis in humans in sub-Saharan Africa(BioMed Central, 2025-04) Ngwira, Alfred; Manda, S.O.M. (Samuel); Karimuribo, Esron Daniel; Kimera, Sharadhuli IddiBACKGROUND : Tuberculosis (TB) in cattle negatively affects the cattle economy in Africa, with zoonotic TB posing drug-resistance issues in humans. The burden of TB in cattle and zoonotic TB in humans in sub-Saharan Africa (SSA) is not well understood. This study aimed to determine the prevalence of both TB in cattle and zoonotic TB in humans in SSA through meta-analysis. METHODS : Research on TB prevalence was sourced from multiple databases. A random effects meta-analysis model estimated TB prevalence in SSA and its regions, while meta-regression identified risk factors. The analysis included 114 studies for cattle and 59 for humans. RESULTS : The estimated TB prevalence in cattle was 5.06% (95% CI: 3.76–6.78), with a higher burden in West Africa. The prevalence was greater on farms than at abattoirs. Among humans, M. bovis prevalence was 0.73% (95% CI: 0.53–1.01), increasing to 1.56% (95% CI: 1.04–2.33) in TB incident cases, especially in the West and East Africa. Higher prevalence was noted among livestock workers, and in drug-resistant cases. Significant factors influencing TB prevalence varied for cattle and humans, including country, diagnostic methods, and study populations. CONCLUSION : Focusing interventions on farms and livestock workers could help reduce the disease burden.Item Factors that affected South African students’ sense of self-perceived academic competence during the COVID-19 lockdown and the rapid transition to online learning(MDPI, 2025-02) Law-Van Wyk, Eloise; Visser, Maretha; Masenge, Andries; eloise.law-vanwyk@up.ac.zaThe COVID-19 pandemic lockdown restrictions had significant impacts on the well-being and academic functioning of students worldwide. When universities closed campuses and moved teaching and learning online, students faced numerous challenges. The researchers conducted a study to establish which factors most affected South African students’ academic competence during the initial months of lockdown and the shift to online learning. Using an online survey that focused on students’ wellness, perceived academic competence and coping behaviour, data were collected from 3239 university students. Multiple linear regression showed that students’ subjective sense of intellectual wellness, coping behaviour, satisfaction with support from the university, and mental health were strong predictors of academic competence. Other factors that influenced students’ academic competence were emotional and spiritual wellness, perceptions of safety and security, and hopefulness. Females, undergraduates, and Faculty of Law students reported higher perceptions of academic competence. These findings have practical implications for universities as they identify factors that contribute to students’ academic competence, especially during times of crisis and online learning. Academic and support services staff at universities may find the findings valuable when developing policies to provide appropriate resources and services to promote and sustain students’ academic functioning.Item Prevalence and associated factors of immunization among under-five children in Somalia(BioMed Central, 2025-03) Belay, Denekew Bitew; Ali, Mahad Ibrahim; Chen, Ding-Geng (Din); Jama, Umalkhair AbdiBACKGROUND : Children worldwide can live lives free from various illnesses and disabilities due to vaccination. For instance, vaccination has eliminated smallpox, a deformative and frequently fatal illness that claimed an estimated 300 million lives in the twentieth century. However, due to a lack of access to immunization and other health services, 14.3 million infants in 2022 still did not receive their first dose of the Diphtheria-Tetanus-Pertussis (DTP) vaccine, and an additional 6.2 million received only a portion of the scheduled dose. This study aimed to assess prevalence and determinant factors of immunization among under-five children in Somalia using Somalia Health and Demographic Survey (SHDS) Data. METHODS : The study design was cross-sectional, utilizing the SHDS 2020 data. A total of 3916 under-five children who fulfilled the inclusion criteria were included in this study. Count regression models were employed to explore factors associated with the number of vaccinations received per child. RESULTS : In this study, 9.14% of children did not receive any vaccination during their childhood. Different candidate count regression models were compared. Using AIC and BIC, the Negative-binomial (NB) regression model was found to be the best fit. From this model, we found that women ages 20–24 (IRR = 1.192, 95% CI: 1.083, 1.313) and 25–29 (IRR = 1.180, 95% CI: 1.068, 1.305) had a higher number of vaccinations per child compared to women in the 15–19 age group. Women who attended primary education (IRR = 1.090, 95% CI: 1.034, 1.150) and secondary education (IRR = 1.157, 95% CI: 1.058, 1.266) had a higher number of vaccinations per child compared to uneducated women) also correlated with increased vaccination Parity (IRR = 1.090, 95% CI: 1.031–1.153), and wealth quantile (IRR = 1.110, 95% CI: 1.012, 1.217) positively influenced vaccination attendance. Regional disparities were also found to be significant, with Togdheer, Sool, Sanaag, Bari, Nugaal, Bay, Bakool, Mudug, Hiiraan and Galgaduud significantly different from Awdal region. In Negative-Binomial, age, region, residence, educational level, wealth quantile, child size at birth, parity and birth order emerged as key predictors, revealing complex determinants of vaccination utilization in Somalia. CONCLUSIONS : A large proportion of children did not complete the full vaccination schedule. Socio-demographic factors, such as age, region, residence, educational level, wealth quantile, child size at birth, parity, and birth order, had a significant impact on the number of children vaccinated in Somalia. These findings underscore the importance of targeted interventions for addressing these factors. Implementing initiatives based on these conclusions has the potential to enhance vaccination coverage and child health outcomes.Item Improved runs-rules precedence charts for monitoring the process location parameter(Springer, 2025-04) Human, Schalk William; Malela-Majika, Jean-Claude; Kritzinger, Pierre; malela.mjc@up.ac.zaRuns-rules are typically incorporated into control charts to increase their sensitivity to detect small process shifts. However, a drawback of this approach is that the resulting charts are unable to detect large shifts quickly. In this paper, improved runs-rules are introduced to the nonparametric precedence chart to address this limitation by maintaining the sensitivity to small process shifts, while improving the ability to detect large shifts in the process. Performance comparisons between the proposed precedence charts and the precedence charts with standard runs-rules are made in terms of their respective run-length characteristics. The results reveal that the precedence charts with improved runs-rules are superior to the competing charts in detecting large shifts in the process, while maintaining the same sensitivity in the detection of small shifts. A real-life example from the engineering field is given to demonstrate the application and implementation of the new charts.Item A power-cardioid candidate for wind direction modelling motivated by two South African case studies(Springer, 2025-04) Van Wyk-de Ridder, Delene; Rad, Najmeh Nakhaei; Arashi, Mohammad; Ferreira, Johan; Bekker, Andriette, 1958-; johan.ferreira@up.ac.zaWind energy claims a positive image globally; therefore, accurate modelling of wind direction at generation sites accurately can enhance the potential of this green energy source. The uncertain nature of wind direction can be modelled through probability distributions; in this paper, we propose a flexible yet simple distribution, namely the Power-Cardioid distribution, as an alternative and implementable candidate to model wind direction. After discussing some characteristics, the performance of the Power-Cardioid distribution is evaluated via a simulation study and applied to datasets of two wind farms in South Africa. The numerical results demonstrate that this distribution is a promising and exciting new candidate compared to well-known models within circular statistics.Item Development and validation of a knowledge, attitudes and practices (KAP) questionnaire for healthcare professionals on environmental sustainability in healthcare in Southern Africa(F1000 Research Ltd, 2024-10) Lister, Helga Elke; Mostert, Karien; Botha, Tanita; Field, Emma; Knock, Danté; Mubi, Natasha; Odendaal, Stefani; Rohde, Megan; Maric, FilipBACKGROUND: The triple planetary crisis of climate change, environmental pollution, and biodiversity loss is increasingly driving poor health outcomes worldwide. Healthcare systems and services are often not environmentally sustainable and compound the problem, while healthcare professionals are also recognised as key leaders in advancing sustainable healthcare. To adopt this leadership position, healthcare professionals’ knowledge, attitudes, and practices regarding environmental sustainability in healthcare must be established. This article reports the development and validation of a new instrument for this purpose that corresponds to the specificities of the Southern African context. METHODS: Questionnaire development followed a seven-stage process. Information was obtained from a 2021 study titled ‘South African Healthcare Professionals’ Knowledge, Attitudes, and Practices Regarding Environmental Sustainability in Healthcare: A Mixed Methods Study’ to develop the instrument. Information was also sourced from the literature regarding environmental sustainability and healthcare to generate the first questionnaire with 29 items. The following stages included two rounds of expert input, separated by a pilot study with the target population to receive feedback regarding the instrument’s structure, relevance, and length. Content validity was determined through statistical analysis. RESULTS: Feedback was received from nine experts in stage two and 13 pilot study participants in stage four and incorporated to improve the questionnaire. In stage six, the questionnaire was rated by seven experts. The content validity index of the questionnaire was calculated at two different stages, after which the indices were compared. Following a final edit, the questionnaire has 24 questionnaire items. The closing analysis calculated the scale content validity index average (S-CVI/Ave) of 0,922; this indicates that the final questionnaire has excellent content validity. CONCLUSION: A questionnaire that assesses the knowledge, attitudes and practices of healthcare professionals regarding environmental sustainability in Southern Africa has been developed and validated. This questionnaire can now be used for further studies in Southern Africa.Item Robust PCA with Lw,∗ and L2,1 norms : a novel method for low-quality retinal image enhancement(MDPI, 2024-07) Likassa, Habte Tadesse; Chen, Ding-Geng (Din); Chen, Kewei; Wang, Yalin; Zhu, WenhuiPlease read abstract in the article.