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

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Now showing 1 - 20 of 545

Multiscale decomposition of spatial lattice data for hotspot detection
(South African Statistical Association, 2024-03) Stander, René; Fabris-Rotelli, Inger Nicolette; Chen, Ding-Geng (Din
Hotspot detection in spatial analysis identifies geographic areas with elevated event rates, facilitating more effective policy interventions aimed at reducing such incidents. In the current literature, several methods have been used to detect hotspots such as measures for local spatial association and spatial scan methods. However,the performance of these methods is limited for small-scale hotspots as well as spatial domains where the number of areas is small. In this work, we propose anew approach, making use of the Discrete Pulse Transform (DPT) to decompose spatial lattice data along with the multi-scale Ht-index and the spatial scan statistic as a measure of saliency on the extracted pulses to detect significant hotspots. The proposed method outperforms the well-used local Getis-Ord statistic in a simulation study, especially on small-scale hotspots. The method is also illustrated on South African COVID-19 cases and South African crime data.
Does wind affect the orientation of vegetation stripes? A copula-based mixture model for axial and circular data
(Wiley, 2025-07) Mingione, Marco; Lagona, Francesco; Nagar, Priyanka; Von Holtzhausen, Francois Victor; Bekker, Andriette, 1958-; Schoombie, Janine; Le Roux, Peter Christiaan
Motivated by a case study of vegetation patterns, we introduce a mixture model with concomitant variables to examine the association between the orientation of vegetation stripes and wind direction. The proposal relies on a novel copula-based bivariate distribution for mixed axial and circular observations and provides a parsimonious and computationally tractable approach to examine the dependence of two environmental variables observed in a complex manifold. The findings suggest that dominant winds shape the orientation of vegetation stripes through a mechanism of neighboring plants providing wind shelter to downwind individuals.
Modeling the output from a commercial chemical process using regression models from survival analysis
(Taylor and Francis, 2025) Coetzer, R.L.J.; De Waal, Daan; Smuts, M.; Visagie, I.J.H.
This article is concerned with the modeling of the gas output of a commercial chemical plant using the coal sources as predictor variables. We consider the use of two models to incorporate these predictors; the Cox proportional hazards and accelerated failure time regression models. These models are chosen for their simplicity and for the ease with which the effects of explanatory variables can be interpreted. The contribution of this article lies therein that these models are used in the current context for the first time. We show, using both graphical and formal hypothesis testing procedures that these models (with a Weibull baseline distribution) fit observed gas production data well. We provide a discussion of the interpretation of the estimated model parameters and we comment on how these estimates can be of substantial practical value. The large scale of production from the chemical plant in question ensures that potential cost savings and increases in production associated with more accurate models are of great practical importance.
Neutrosophic Birnbaum-Saunders distribution with applications
(Elsevier, 2026-01) Razmkhah, Mansooreh; Arashi, Mohammad; Bekker, Andriette, 1958-; Marques, Filipe J.
This paper presents an extension of the Birnbaum-Saunders distribution through the incorporation of neutrosophic concepts, aimed at effectively addressing data that is characterized by imprecision, uncertainty, and incompleteness. Our model delivers maximum likelihood parameter estimates, effectively capturing the complete spectrum of interval-based values without compromise. We showcase its benefits in industrial and environmental applications, emphasizing its effectiveness in analyzing uncertain data within real-world scenarios, surpassing traditional statistical methods. HIGHLIGHTS • Proposed neutrosophic Birnbaum-Saunders model for indeterminate interval data. • Novel parameter estimation approach for neutrosophic Birnbaum-Saunders model. • New insights into modelling neutrosophic interval data in environmental studies.
Countermovement jump kinetic impairments in elite athletes before and after ACL injury : force-time waveform versus discrete kinetic analysis
(Wiley, 2025-05) De Franca, Cassidy; Jordan, Matthew J.; Botha, Tanita; Bayne, Helen
Pre-injury and post-injury countermovement jump (CMJ) force-time data were obtained for elite athletes 6 months after anterior cruciate ligament surgery (ACLR). Jump kinetics were analysed using a traditional phase-specific approach, and force-time data of the CMJ waveform were analysed using statistical parametric mapping (SPM). Elite athletes (n = 10; female n = 6, age = 22.0 ± 3.5 years, mass = 75.9 ± 11.5 kg) performed CMJ testing before (T0) and after ACLR (T1; 24 ± 3 weeks post-surgery). Differences in discrete and continuous metrics were analysed for (1) within-limb differences between T1 and T0 and (2) between-limb differences at T1 and T0. Lower involved limb propulsive impulse (T1: 6.4 ± 1.6 N∙s/kg; T0: 7.7 ± 1.4 N∙s/kg, p = 0.002) and peak force (T1: 6.4 ± 1.6 N/kg; T0: 7.7 ± 1.4 N/kg, p = 0.002) were found after ACLR compared to baseline. After ACLR (T1), lower involved limb propulsive impulse was found compared to the uninvolved limb (involved: 1.26 ± 0.54 N∙s/kg; uninvolved: 1.58 ± 0.56 N∙s/kg, p = 0.007). SPM analysis revealed specific within-limb force loss, notably reduced involved limb propulsion force at T1 compared to pre-injury at T0 (p < 0.001) between 92% and 99% of the CMJ (end of propulsion) and between 36% and 37% of the CMJ (i.e., late unweighting to braking phase transition). SPM analysis revealed within-limb CMJ force loss that was not seen with the discrete analysis, highlighting the complementary value of SPM waveform analysis alongside discrete analysis to identify neuromuscular impairments in stretch-shortening-cycle function in elite athletes after ACLR.
Discrete mode-mixtures of unimodal positive distributions with an application to solar energy in South Africa
(Springer, 2025-09) Bekker, Andriette, 1958-; Otto, A.F.; Punzo, A.; Tomarchio, S.D.; Ferreira, Johannes Theodorus; andriette.bekker@up.ac.za
Comprehensive earth science studies consistently yield complex datasets seldom adequately represented by straightforward parametric distributions. In this paper, we introduce a discrete mode-mixture (DMM) model, motivated by the formulation of the mean mixture paradigm via the compounding method. Here, unimodal positive support mode-parameterized beta and gamma distributions represent the basic component, but with the superposition of a discrete random component on the mode. The probability density functions of the DMM models are derived in closed-form expressions, and specific characteristics are investigated. This alternative viewing of a mixture on the mode paves the way for alternative models and provides natural leverage on separation in data. With an emphasis on a solar dataset and a benchmark dataset, the performance of the proposed models is compared with that of well-known models.
Namibian healthcare professionals’ knowledge, attitudes and practices regarding environmental sustainability in healthcare
(MDPI, 2025-05) Lister, Helga Elke; Mostert, Karien; Ramkilawon, Gopika Devi; Oelschig, Cathrine; Ntiyane, Olwethu; Richardt, Erika; Da Silva Rocha, Deonelia Paulo; Sheerin, Savannah; Phaahla, Tshepang; Ashipala, Daniel; Pretorius, Louise; Munangatire, Takaedza; Maric, Filip
Among the many actions required to avert further intensification of today’s social, ecological and health crises is also the improvement of healthcare’s environmental sustainability, including in countries particularly vulnerable to such crises. The present study aimed to identify Namibian healthcare professionals’ knowledge, attitudes and practices, along with barriers and educational needs, as a foundation for context-relevant interventions. The study used a non-experimental, descriptive quantitative research design with an existing validated cross-sectional questionnaire as its data collection tool. Both purposive and snowball sampling were used to select healthcare professionals (n = 71) to participate in the quantitative online questionnaire. R (version 4.2.1) software was used to analyse the data from the completed questionnaires. The results showed that the Namibian healthcare professionals participating in this study have basic knowledge of and positive attitudes toward environmental sustainability in healthcare. However, various barriers to implementing strategies towards environmental sustainability exist that currently prevent the implementation of relevant practices. These should be overcome by the Namibian health system by providing the necessary frameworks, policies, measures and resources to drive improvements in environmental sustainability. Additionally, future and current healthcare professionals must receive training across all professional education levels to enable implementation in practice and effective advocacy and planetary health promotion.
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.za
BACKGROUND : 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.
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.
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, Michael
No abstract available.
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.za
Entropy 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.
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.za
The 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.
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 Nakhaei
BACKGROUND : 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.
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 Bitew
BACKGROUND : 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.
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.
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.
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, Saralees
In 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.
Additive modeling of zonal level crop production in Ethiopia
(Nature Research, 2025-04) Mare, Yidnekachew; Zewotir, Temesgen; Belay, Denekew Bitew
Crop 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.
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.za
There 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.
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.

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