Research Articles (Statistics & Population Studies)

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Screening for retinopathy of prematurity (ROP) in South Africa: data from a newly established prospective regional register
(BMJ Publishing Group, 2025) Jordaan, Esmè; van der Lecq, Tshilidzi; Rhoda, Natasha
Objective Retinopathy of prematurity (ROP) registers enable population-based studies to monitor ROP screening programmes to improve their effectiveness. The aim of this study was to determine the frequency of ROP and the coverage of screening in a South African cohort using a prospective ROP South African (ROPSA) register. Methods and analysis Infants born from 1 May 2022 to 31 January 2023 and screened prospectively for ROP at five neonatal intensive care units in Cape Town were included. The screening criteria were a gestational age (GA) <32 weeks or birth weight (BW) <1250 g. Data were extracted from the ROPSA register and analysed. Results 696 of 1154 (60.3%) eligible infants were screened, almost half of whom (45.7%) did not complete screening. ROP was detected in 220 infants (31.6%, 95% CI 28.3% to 35.3%), 7 (1.0%) of whom required treatment. Infants with incomplete screening had a lower mean GA than those who completed screening; 28.7 (SD 1.6, range 25-33) and 29.1 (SD 1.7, range 24-36) weeks, respectively (p=0.004) and a lower mean BW; 1048 (SD 203, range 650-1690) g and 1108.5 (SD 227, range 640-1840) g, respectively (p<0.001). Conclusions Data from the ROPSA register on the frequency of any ROP and treatment-requiring ROP may be biased due to low screening coverage and high incomplete screening. Reasons need to be explored and corrective interventions initiated. The ROPSA register will enable the impact of these interventions to be monitored. The findings of this study will contribute to the ongoing revision of South African national ROP screening guidelines.
Autoregressive moving average modelling of TESS photometry of massive stars
(Oxford University Press, 2025) Koen, Chris
Standard statistical time-series analysis methods developed for observations regularly spaced in time are applied to measurements of 30 massive stars. Two Transiting Exoplanets Survey Satellite orbits of observations of each of the stars are analysed using this time-domain methodology. It is found that the majority of light curves do not exhibit quasi-periodicities, i.e. the variability is fully aperiodic. The effective temperature and gravity can be used to predict with good accuracy the presence/absence of quasi-periodicities. Frequencies have a quadratic dependence on the effective temperature. The calculation of characteristic frequencies is also discussed. It is shown that the use of inappropriate spectral forms for this purpose may lead to biased results.
Independent risk factors associated with a history of exercise associated muscle cramps (EAMC) among 21460 cycling race entrants (SAFER XXXVI): a descriptive cross-sectional study
(Revista Brasileira de Fisioterapia, 2026) Jordaan, Esme; Pohl, Carey; Schwellnus, Martin
Background: There is limited research on cyclists with a history of exercise associated muscle cramps (hEAMC) defined as muscle cramping (painful, spontaneous, sustained spasm of a muscle) during or after cycling. Objective: To determine the epidemiology, clinical characteristics, and risk factors associated with hEAMC in cyclists taking part in a mass participation cycling event. Methods: 21,460 race entrants from the 2016 Cape Town Cycle Tour completed an online questionnaire, which is based on the guidelines for recreational exercise participation from the European Association of Cardiovascular Prevention and Rehabilitation [EACPR]. The main outcome measures were: the lifetime prevalence hEAMC (%; 95% confidence intervals), independent risk factors (adjusted for age and sex) associated with hEAMC (history of chronic disease, history of allergies, history of chronic medication use, history of medication use before and during race, history of cycling injuries, and cycling training/racing variables). Poisson regression was used to calculate the prevalence (%) of the variables of interest, with 95% confidence intervals. Results: The retrospective lifetime prevalence of hEAMC was 30.51%. EAMC in cyclists affects mainly the quadriceps muscles and occurs in the 4th quarter during a race. Novel independent risk factors associated with an increased risk of hEAMC in cyclists were: increased number of years participating as a recreational cyclist (PR=1.03 per 5 years increase; p<0.0001), a higher chronic disease composite score (PR=1.36 times increased risk for every 2 additional chronic diseases; p<0.0001), a history of any allergies (PR=1.18; p<0.0001), medication use before or during event (PR=1.41; p<0.0001) a history of an acute (PR=1.30; p<0.0001) and gradual onset injury (PR=1.29; p<0.0001). Conclusion: Our study identified novel independent risk factors associated with a hEAMC. These results, in combination with other known risk factors, could assist future targeted prevention programmes and the management of EAMC in recreational cyclists.
A review and comparison of methods of parameter estimation and inference for heteroskedastic linear regression models
(Taylor and Francis Ltd., 2025) Farrar, Thomas J.; Blignaut, Rénette Julia; Luus, Retha; Steel, Sarel J.
This article reviews methods of parameter estimation and inference in the linear regression model under heteroskedasticity. Several approaches to feasible weighted least squares estimation of the parameter vector are reviewed, along with various heteroskedasticity-consistent covariance matrix estimators, which are usually designed with inference as the end goal. A Monte Carlo experiment is designed to evaluate the ability of the reviewed methods to estimate three quantities: the variances of the random errors, the parameter vector, and the standard error of the ordinary least squares estimator thereof. Results of the experiment show that the homoskedastic variance estimator performs well at estimating error variances even in the heteroskedastic data-generating processes studied. Feasible weighted least squares approaches perform best for estimation of the parameter vector, whereas heteroskedasticity-consistent covariance matrix estimators perform best for estimation of the standard error thereof. This motivates a search for a method that would perform well in all three respects.
Women’s and girls’ sexual empowerment differs by geographical context: a population-based validation study
(BioMed Central Ltd, 2025) Omoluabi, Elizabeth; Wood, Shannon; Dozier, Jessica
Objective: To validate a sexual empowerment sub-scale of the Women’s and Girls’ Sexual and Reproductive Empowerment Index (WGE-SRH) across eight countries in sub-Saharan Africa and Asia, and compare sexual empowerment across these contexts. Methods: This study leverages cross-sectional, population-based survey data collected among women of reproductive age in Burkina Faso (n = 4,012), Côte d’Ivoire (n = 2,278); Kongo Central, Democratic Republic of the Congo (DRC (n = 1,097)); Kinshasa, DRC (n = 1,143); Rajasthan, India (n = 4,004); Kenya (n = 5,454); Kano, Nigeria (n = 780); Lagos, Nigeria (n = 804); Niger (n = 2,286); and Uganda (n = 2,228) to validate eight sexual empowerment measures via confirmatory factor analysis. Overall scores of the validated measures were descriptively examined across settings. Findings: Final models confirm the theoretical structure of the sexual empowerment measure, including two- dimensions: “existence of choice” and “exercise of choice”, each comprised of three items, with moderate internal consistency ranging from 0.59 to 0.69. Factor loadings, goodness-of-fit, and percent agreement varied in Rajasthan, India compared to sub-Saharan African settings. Marked variations were seen across sites in women’s perceptions of their partners’ responses to refusing sex, as well as their own confidence in voicing when and when not to have sex. Conclusion: This measure was developed in sub-Saharan Africa and works well for the population that it was designed to serve, however, cannot be extrapolated to other settings. To comprehensively capture the dynamic nature of sexual empowerment, future research is needed to examine measures across cultures and time. Validation across diverse settings opens avenues for holistic examination of positive sexual health, including factors that enhance women’s sexual empowerment and rights.
Amplitude and phase changes in TESS photometry of five short period weak-lined T Tauri stars
(Oxford University Press, 2024) Koen, Chris
The statistical technique ‘complex demodulation’ (CDM) is used to track the amplitude and phase changes of periodicities in five naked T Tauri stars. The periodicities are most likely caused by dark spots on the stellar surfaces, which are rotated into and out of view. Two of the stars (CD-56 1438, CD-72 248) show two independent periodicities, probably due to being binary weak-lined T Tauri stars. Two different low-pass filters, operating, respectively, in the frequency and time domains, are used as part of the CDM methodology. Statistical aspects of the estimated amplitudes and phases are investigated in some detail: in particular, expressions are derived for standard errors and for possible biases. A large variety of different types of amplitude and phase changes are found, including approximately linear or quadratic, abrupt level shifts, pulses, and oscillatory. Long term changes in amplitudes are aperiodic, but mimic long-term cycles.
Agricultural involvement amongst smallholders of south af-rica: evidence from ghs 2015 and ghs 2018
(Union for African Population Studies, 2024) Mbamba, Faith Sabelo; Nsengiyumva, Philomene
The smallholding is central to livelihood diversifications that drive economic growth in non-metropolitan settlements. This gained recognition in the Zero Hunger Challenge, Agenda 2063, SDGs, and NDP 2030 for South Africa. Agricultural support programmes must be well-defined and transparent to rural communities. Subsequently, for smallholders to enact their role, there should be a clear reflection of the constraints they encounter. This study sought to ascertain factors influencing the agricultural involvement of smallholders heading households in rural settlements of South Africa. The secondary data from the 2015 and 2018 General Household Survey (GHS) were utilized and retrieved from the Statistics South Africa website. SPSS software version 28 and Microsoft Excel were exploited for data analysis using the Chi-square test and binary logistic regression. The findings established that younger household heads are more agriculturally involved and do not have tertiary education to market occupations, particularly in the off-farm sector, where food production is their source of livelihood. This study shows that socioeconomic and sociodemographic characteristics play a significant role in determining agricultural involvement. Accordingly, it contends that constraints faced by small-scale food producers are urgently revisited to ensure adequate farm resources’ accessibility and support, especially for the poor youth in rural area.
Longitudinal impact of past-year reproductive coercion on contraceptive use dynamics in Sub-Saharan Africa: evidence from eight population-based cohorts
(Elsevier Ltd, 2024) Omoluabi, Elizabeth; Wood, Shannon N; Thomas, Haley L
Background: Reproductive coercion (RC) is a type of abuse where a partner intentionally attempts to interfere with fertility through deception or violence, often by manipulating one's contraceptive use or reproductive decision-making. Cross-sectional studies on the magnitude of RC across sub-Saharan Africa have noted associations with contraceptive use. No studies have longitudinally examined RC experiences as related to future contraceptive dynamics, including discontinuation or forgoing use altogether. Methods: Two rounds of longitudinal population-based cohorts across eight sites in sub-Saharan Africa, from November 2020 to January 2023, were used to prospectively examine past-year RC's impact on future contraceptive dynamics (discontinuation and switching vs. continuation for contraceptive users at baseline; adoption vs. continued non-use for contraceptive non-users at baseline) using bivariate and multivariable multinomial and logistic regression. Findings: Minimal differences in women's past-year RC experiences were observed over a two-year period. In many settings, RC prevalence decreased. Only in Uganda did past-year RC increase between rounds (15.8% to 17.8%). RC's impact on contraceptive dynamics over one year differed by setting. In Burkina Faso, women with past-year RC had a three-fold increased risk of discontinuing contraception, as compared to continuing (RRR = 2.63; 95% CI = 1.28–5.42; p<0.01). In Uganda, past-year RC was marginally associated with reduced odds of contraceptive adoption, compared to continued non-use (p<0.1). Interpretation: In this first longitudinal study of RC, trajectories varied across settings, as did RC's impact on contraception, affirming the importance of context. Future work should clarify RC trajectories and drivers thereof. Providers must be aware of RC leading to potential discontinuation. Contraceptive provision must be flexible and reflect women's life circumstances, including partner dynamics. Funding: This work was supported, in whole, by the Bill & Melinda Gates Foundation [ INV-046501 and INV-009639]. Under the grant conditions of the Foundation, a Creative Commons Attribution 4.0 Generic License has already been assigned to the Author Accepted Manuscript version that might arise from this submission.
A qualitative exploration of reproductive coercion experiences and perceptions in four geo-culturally diverse sub-Saharan African settings
(Elsevier Ltd, 2024) Omoluabi, Elizabeth; Thomas, Haley L.; Bell, Suzanne O; Karp, Celia
Reproductive coercion (RC) is any intentional behavior that interferes with another’s reproductive decision-making or pregnancy outcome. This study aims to qualitatively examine RC experiences and perceptions among women and men in Ethiopia, Nigeria (Kano and Anambra States), and Uganda. This is a secondary analysis utilizing qualitative data from the Women’s and Girls’ Empowerment in Sexual and Reproductive Health study. Across sites, focus group discussions (38 groups; n=320 participants) and in-depth interviews (n=120) were conducted, recorded, and transcribed. Transcripts were loaded into Atlas.ti, and quotes describing experiences of reproductive control or abuse were coded as “reproductive coercion.” RC quotes were input into a matrix for thematic analysis. Emergent RC themes included indirect reproductive pressures, direct family planning interference, concurrent experiences of violence, and responses to RC. Indirect reproductive pressures included tactics to both promote and prevent pregnancy, while direct interference centered on pregnancy promotion. Women who were not compliant with their partners’ reproductive demands were often subjected to violence from multiple actors (i.e., parents, in-laws, community members) in addition to their partners. Despite concurrent forms of violence, women across sites resisted RC by using contraceptives covertly, choosing to abort, or leaving their abusive partnerships. Women and men across sites indicated that men were highly influential in fertility. RC behaviors were a mechanism of control over desired reproductive outcomes, which were often rooted in perceptions of childbearing as social status. Findings indicate a need for more nuanced community interventions targeting social norms, as well as improved RC screening and response within health services.
Pre-race self-reported medical conditions and allergies in 133 641 Comrades ultramarathon (90km) runners - SAFER XXIII
(The Physician and Sportsmedicine, 2023) Jordaan, Esme; Brill, Stephan; Schwellnus, Martin; Sewry, Nicola
Objectives: To determine the prevalence of self-reported pre-race chronic medical conditions and allergies in ultramarathon race entrants and to explore if these are associated with an Increased risk of race-day medical encounters (MEs). Methods: Data from two voluntary open-ended pre-race medical screening questions (Q1 – history of allergies; Q2 - history of chronic medical conditions/prescription medication use) were collected in 133 641 Comrades Marathon race entrants (2014-2019). Race-day ME data collected prospectively over 6 years are reported as incidence (per 1000 starters) and incidence ratios (IR: 95%CI’s).
Global warming and psychotraumatology of natural disasters: the case of the deadly rains and floods of April 2022 in South Africa
(Annales Médico-psychologiques, revue psychiatrique, 2023) Bouchard, Jean-Pierre; Pretorius, Tyrone B; Kramers-Olen, Anne L
Climate change and global warming have led to an increased incidence of flooding across the world. Against the backdrop of the recent devastating floods in the Kwazulu-Natal province of South Africa, this paper explores psychotraumatology of natural disasters. In particular, we explore the impact of internal migration in South Africa, as well as apartheid spatial planning and inequality on the consequences of the flooding. We also focus on the psychotraumatology resulting from flooding, in general, and in particular on the victims of the flooding in the KwaZulu-Natal province of South Africa. We conclude that the psychopathological consequences of such natural disasters are ignored even though they seriously affect the people concerned. The development of specific trainings for psychologists in psychotraumatology and the care of victims should be a priority in the future.
Boys or girls? Sex preferences declared in African and South-Asian demographic surveys
(Elsevier, 2023) Garenne, Michel; Stiegler, Nancy; Bouchard, Jean-Pierre
In this interview with Jean-Pierre Bouchard, demographers Michel Garenne and Nancy Stiegler explore sex-preferences for girls or for boys expressed by women who responded to DHS surveys in 29 African and 10 Asian countries. The IPUMS/DHS database was used for statistical analysis, bringing together 140 surveys and 2.5 million women aged 15–49. Overall, two-thirds of women were in favor of a balanced number of girls and boys or were indifferent to the composition of the family. In 20.8% of cases, they preferred to have more boys, and in 12.6% of cases they preferred to have more girls. These proportions vary considerably between countries, and were influenced by local culture, religion, level of education, household wealth, and to a small extent by urban residence. Sex preferences were also influenced by family composition. These preferences are likely to change rapidly over time. Among the countries analyzed, eight expressed preferences for more girls, all located in sub-Saharan Africa, and particularly in southern Africa. These preferences could have many consequences, demographic, psychological and social.
Causes and patterns of morbidity and mortality in Afghanistan: Joint estimation of multiple causes in the neonatal period
(Springer, 2014) Adegboye, Oyelola A.; Kotze, Danelle
This paper focuses on investigating the leading cause(s) of death and preventable factors in Afghanistan, using data from verbal autopsies of infant deaths. We are of the view that the presence of a disease in a person may increase the risk of another disease that may contribute to the death process. The influence of individual- and community-level variables on infant morbidity and mortality in Afghanistan is examined. The results of this study suggest the existence of multiple causes of death in the Afghanistan Mortality Survey (AMS). In Afghanistan, complications of pregnancy are clearly a problem and must be adequately improved.
On multiple classes of gamma-ray bursts, as deduced from autocorrelation functions or bivariate duration/hardness ratio distributions
(Oxford University Press, 2012) Koen, C; Bere, A
Autocorrelation functions (ACFs) of 119 gamma-ray bursts (GRBs) monitored by the Burst Alert Telescope (BAT) on Swift are calculated. Contrasting with previous results for smaller numbers of bursts from other missions, the widths of the ACFs are not bimodally distributed. Although the distribution appears slightly asymmetrical, underlying mixtures of distributions can also probably be ruled out. Factors contributing to differences between the results presented here, and those in the literature, may include the differences in energy passbands used, and the superior sensitivity of the BAT instrument (which affects e.g. the redshift distribution of the detected GRB). The second part of the paper is concerned with the fitting of mixtures of bivariate Gaussians to the joint duration/hardness ratio data of 325 GRBs. A careful analysis confirms that a three-component mixture is the statistically most acceptable, but it is shown that the implied marginal distribution of the hardness ratios does not fit the data very well. It is also stressed that mixture components cannot automatically be assumed to represent different classes of GRBs. The point is illustrated by showing two substantially different, but statistically almost equivalent, mixture models for the distribution of 571 BAT-determined GRB durations.
Symptom number and reduced preinfection training predict prolonged return to training after sars-cov-2 in athletes: Aware IV
(Lippincott, Williams & Wilkins, 2023) Snyders, Carolette; Schwellnus, Martin; Jordaan, Esme
Symptom Number and Reduced Preinfection Training Predict Prolonged Return to Training after SARS-CoV-2 in Athletes: AWARE IV. Med. Sci. Sports Exerc., Vol. 55, No. 1, pp. 1-8, 2023. Purpose: This study aimed to determine factors predictive of prolonged return to training (RTT) in athletes with recent SARS-CoV-2 infection. Methods: This is a cross-sectional descriptive study. Athletes not vaccinated against COVID-19 (n = 207) with confirmed SARS-CoV-2 infection (predominantly ancestral virus and beta-variant) completed an online survey detailing the following factors: demographics (age and sex), level of sport participation, type of sport, comorbidity history and preinfection training (training hours 7 d preinfection), SARS-CoV-2 symptoms (26 in 3 categories; “nose and throat,” “chest and neck,” and “whole body”), and days to RTT. Main outcomes were hazard ratios (HR, 95% confidence interval) for athletes with versus without a factor, explored in univariate and multiple models. HR < 1 was predictive of prolonged RTT (reduced % chance of RTT after symptom onset). Significance was P < 0.05. Results: Age, level of sport participation, type of sport, and history of comorbidities were not predictors of prolonged RTT.
Trauma and PTSD in prisons and corrections
(Elsevier, 2023) Fovet, Thomas; Villa, Clément; Bouchard, Jean-Pierre
Post-traumatic stress disorder (PTSD), and particularly complex PTSD, is over-represented in prisons and corrections. In this interview with Jean-Pierre Bouchard, Thomas Fovet, Cle ́ ment Villa, Bettina Belet, Fanny Carton, Timothe ́ e Bauer, Suzanne Buyle-Bodin and Fabien D’Hondt draw on their clinical experience and recent epidemiological research to provide an overview of the issue. The clinical aspects specifically found in the prison environment, especially the questions of comorbid psychiatric and substance use disorders or PTSD in perpetrators of violent crime, are developed. The current state of knowledge regarding the management of post-traumatic symptoms in prison is also discussed and put into perspective with daily practice.
Factors associated with patellofemoral pain in recreational road cyclists: A cross-sectional study in 59953 cyclists – SAFER XXXIII
(Elsevier, 2023) du Toit, François; Schwellnus, Martin; Jordaan, Esme
Patellofemoral pain (PFP) is a common cycling-related injury, and independent factors need to be identified to enable effective injury prevention strategies. We aim to determine factors associated with PFP in cyclists entering mass community-based events. 62758 consenting race entrants completed a pre-race medical questionnaire, and 323 reported PFP. Selected factors associated with PFP (demographics, cycling experience and training, chronic disease history) were explored using multivariate analyses.
Incidence and burden of injury at the Tokyo 2020 Paralympic Games held during the Covid-19 pandemic: A prospective cohort study of 66 045 athlete days
(British Journal of Sports Medicine, 2022) Derman, Wayne; Runciman, Phoebe; Jordaan, Esme
Objective To describe the epidemiology of injuries at the Tokyo 2020 Paralympic Games, including injuries sustained in the new sports of badminton and taekwondo. Methods Injury data were obtained daily via the established web-based injury and illness surveillance system (WEB-IISS; 81 countries, 3836 athletes) and local organizing committee medical facilities (81 countries, 567 athletes).
What are psychiatric disorders of people who are incarcerated in France
(Elsevier, 2022) Bouchard, Jean-Pierre
The presence of detainees suffering from psychiatric disorders has been observed since the birth of the modern prison system, and the numbers have fluctuated since then, depending on the evolution of psychiatric facilities and the French legislative framework. As of January 1, 2022, almost 70,000 people were incarcerated in the 187 French correctional institutions in metropolitan and overseas France. Many psychiatric disorders are over-represented in the correctional population compared to the general population, and they include disorders such as depressive, psychotic, bipolar, post-traumatic stress, and substance abuse disorders together with neurodevelopmental disorders such as attention deficit disorder with/without hyperactivity. In this interview with Jean-Pierre Bouchard, Thomas Fovet and Marion Eck discuss this phenomenon based on recent epidemiological data and their personal experience. Some specific clinical aspects of psychiatry in the correctional environment are also discussed.
Examining inequality of opportunity in the use of maternal and reproductive health interventions in Sierra Leone
(Oxford University Press, 2020) Tsawe, Mluleki; Susuman, Sathiya A.
Poor countries, such as Sierra Leone, often have poor health outcomes, whereby the majority of the population cannot access lifesaving health services. Access to, and use of, maternal and reproductive health services is crucial for human development, especially in developing regions. However, inequality remains a persistent problem for many developing countries. Moreover, we have not found empirical studies, which have examined inequalities in maternal and reproductive health in Sierra Leone.

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