Research Articles (Statistics & Population Studies)
Permanent URI for this collection
Browse
Browsing by Title
Now showing 1 - 20 of 162
Results Per Page
Sort Options
Item The analysis of indexed astronomical time series – X. Significance testing of O − C data(Oxford University Press, 2006) Koen, ChrisIt is assumed that O − C (‘observed minus calculated’) values of periodic variable stars are determined by three processes, namely measurement errors, random cycle-to-cycle jitter in the period, and possibly long-term changes in the mean period. By modelling the latter as a random walk, the covariances of all O − C values can be calculated. The covariances can then be used to estimate unknown model parameters, and to choose between alternative models. Pseudo-residuals which could be used in model fit assessment are also defined. The theory is illustrated by four applications to spotted stars in eclipsing binaries.Item The analysis of indexed astronomical time series – XI. The statistics of oversampled white noise periodograms(Oxford University Press, 2015) Koen, ChrisThe distribution of the maxima of periodograms is considered in the case where the time series is made up of regularly sampled, uncorrelated Gaussians. It is pointed out that if there is no oversampling, then for large data sets, the known distribution of maxima tends to a oneparameter Gumbel distribution. Simulations are used to demonstrate that for oversampling by large factors, a two-parameter Gumbel distribution provides a highly accurate representation of the simulation results. As the oversampling approaches the continuous limit, the twoparameter Gumbel distribution takes on a simple form which depends only on the logarithm of the number of data. Subsidiary results are the autocorrelation function of the oversampled periodogram; expressions for the accuracy of simulated percentiles; and the relation between percentiles of the periodogram and the amplitude spectrum.Item The analysis of indexed astronomical time series – XII. The statistics of oversampled Fourier spectra of noise plus a single sinusoid(Oxford University Press, 2015) Koen, ChrisWith few exceptions, theoretical studies of periodogram properties focus on pure noise time series. This paper considers the case in which the time series consists of noise together with a single sinusoid, observed at regularly spaced time points. The distribution of the periodogram ordinates in this case is shown to be of exponentially modified Gaussian form. Simulations are used to demonstrate that if the periodogram is substantially oversampled (i.e. calculated in a dense grid of frequencies), then the distribution of the periodogram maxima can be accurately approximated by a simple form (at least at moderate signal-to-noise ratios). This result can be used to derive a calculation formula for the probability of correct signal frequency identification at given values of the time series length and (true) signal-to-noise ratio. A set of curves is presented which can be used to apply the theory to, for example, asteroseismic data. An illustrative application to Kepler data is given.Item The analysis of irregularly observed stochastic astronomical time-series – I. Basics of linear stochastic differential equations(Oxford University Press, 2005) Koen, ChrisThe theory of low-order linear stochastic differential equations is reviewed. Solutions to these equations give the continuous time analogues of discrete time autoregressive time-series. Explicit forms for the power spectra and covariance functions of first- and second-order forms are given. A conceptually simple method is described for fitting continuous time autoregressive models to data. Formulae giving the standard errors of the parameter estimates are derived. Simulated data are used to verify the performance of the methods. Irregularly spaced observations of the two hydrogen-deficient stars FQ Aqr and NO Ser are analysed. In the case of FQ Aqr the best-fitting model is of second order, and describes a quasi-periodicity of about 20 d with an e-folding time of 3.7 d. The NO Ser data are best fitted by a first-order model with an e-folding time of 7.2 d.Item Analysis of unmarried adolescents and modern contraceptives initiation in Nigeria: Evidence from 2018 NDHS(MDPI, 2022) Ogujiuba, Kanayo; Ojoniyi, Olaide; Stiegler, NancyNigeria is one of Africa’s most populous countries. Nigeria’s population is expected to exceed 400 million by 2050, putting it among the top five most populous countries in the world. High birth rates, limited contraception use, and early marriage are the main causes of this rapid increase. In Nigeria, adolescents play a substantial role in these issues, with 117 births per 1000 girls aged 15–19 years. Data for this article comes from the 2018 Nigerian Demographic and Health Survey (NDHS). Our sample consisted of 1014 sexually active unmarried adolescents aged 15–19 years. Kaplan Meier’s curve, Log Rank Test, and Cox proportional hazards model were modeled to estimate the parameters at p > 0.05. Findings show that the average time to the first use of modern contraceptives after sexual initiation is two years.Item An assessment of the age reporting in Tanzania population census(Academic Research Publishing, 2012) Mwambene, Eric; Appunni, Sathiya Susuman; Hamisi, Hamisi F.; Lougue, Siaka; Regassa, Nigatu; Ogujiuba, KanayoThe objective of this paper is to provide data users with a worldwide assessment of the age reporting in the Tanzania Population Census 2012 data. Many demographic and socio-economic data are age-sex attributed. However, a variety of irregularities and misstatements are noted with respect to age-related data and sex ratio data because of its biological differences between the genders. Noting the misstatement / misreporting, inconsistence of age data regardless of its significant importance in demographic and epidemiological studies, this study assess the quality of the 2012 Tanzania Population and Housing Census data relative to age. Data were downloaded from Tanzania National Bureau of Statistics. Age heaping and digit preference were measured using summary indices viz., Whipple‟s index, Myers‟ blended index, and Age-Sex Accuracy index. The recorded Whipple‟s index for both sexes was 154.43, where males had the lower index of about 152.65 while females had the higher index of about 156.07. For Myers‟ blended index, the prefrences were at digits „0‟ and „5‟ while avoidance were at digits „1‟ and „3‟ for both sexes. Finally, the age-sex index stood at 59.8 where the sex ratio score was 5.82, and the age ratio scores were 20.89 and 21.4 for males and female respectively. The evaluation of the 2012 Population Housing Censes data using the demographic techniques has qualified the data as of poor quality as a result of systematic heaping and digit preferences/avoidances in recorded age. Thus, innovative methods in data collection along with measuring and minimizing errors using statistical techniques should be used to ensure accuracy of age data.Item Associated risk factors of STIs and multiple sexual relationships among youths in Malawi(PLoS, 2015) Appunni, Sathiya Susuman; Ningpuanyeh, Wilson ChialepehHaving unprotected sex with multiple sexual partners (MSP) is the greatest risk factor for human immunodeficiency virus (HIV) and other sexually transmitted infections (STIs) among youths. Young people with MSPs are less likely to use a condom and the greater the risk for STIs. This study examines the associated risk factors of STIs and multiple sexual partnerships among youths aged 15–24 years. The Malawi Demographic Health Survey 2010 data was used. Out of a sample of 2,987 males and 9,559 females aged 15–24 years, 2,026 males and 6,470 females were considered in the study. Chi square test and logistic regression techniques were performed. Analysis was performed using Statistical Package for Social Sciences (SPSS) version 22.Item Association between pro-inflammatory alleles and allergic phenotypes in Xhosa adolescents(Wiley, 2018) Laurence, Craig; van der Merwe, Lize; Zhang, Guicheng; Le Souef, Peter; Levin, MichaelBACKGROUND: Significant differences exist in the prevalence, spectrum, and severity of allergic diseases between developing and developed countries and between subpopulations within single countries. These discrepancies likely result from a complex interaction between genetic and environmental factors. However, the precise nature of the contribution of ethnicity to genetic differences in the predisposition to allergic disease is not yet fully understood. In particular, there is a paucity of literature regarding the genetic determinants of allergic disease in people of black African origin with little or no genetic admixture. OBJECTIVE: We aimed to analyze associations between 27 single nucleotide polymorphisms (SNPs) and allergy phenotypes in the local Xhosa population. METHODS: A convenience sample of 213 Xhosa teenagers was enrolled at a local high school. Phenotypic data were collected in the form of a symptom questionnaire, skin prick tests for common food and aeroallergens, total serum IgE, and IgE to Ascaris lumbricoides. In addition, genotyping was performed to establish the prevalence of putative pro-inflammatory alleles. RESULTS: We demonstrated several significant associations between polymorphisms and allergy phenotypes. In particular, 2 polymorphisms in the IL-10 gene (IL10 -592A> C and IL10 -1082A> G) and 1 in the IL-4 gene (IL4 -589C> T) showed multiple associations with allergic sensitization and asthma phenotypes. Other polymorphisms, across a multitude of genes with discrepant functions, showed less consistent associations. CONCLUSION: This study represents an important first step in genotype/phenotype association in this population. Further research is required to confirm or refute our findings.Item Associations between human leukocyte antigen class I variants and the Mycobacterium tuberculosis subtypes causing disease(Oxford University Press, 2013) Salie, Muneeb; van der Merwe, Lize; Möller, Marlo; Daya, Michelle; van der Spuy, Gian D.; van Helden, Paul D.; Martin, Maureen P.; Gao, Xiao-jiang; Warren, Robin M.; Carrington, Mary; Hoal, Eileen G.BACKGROUND. The development of active tuberculosis disease has been shown to be multifactorial. Interactions between host and bacterial genotype may influence disease outcome, with some studies indicating the adaptation of M. tuberculosis strains to specific human populations. Here we investigate the role of the human leukocyte antigen (HLA) class I genes in this biological process. METHODS. Three hundred patients with tuberculosis from South Africa were typed for their HLA class I alleles by direct sequencing. Mycobacterium tuberculosis genotype classification was done by IS6110 restriction fragment length polymorphism genotyping and spoligotyping. RESULTS. We showed that Beijing strain occurred more frequently in individuals with multiple disease episodes (P < .001) with the HLA-B27 allele lowering the odds of having an additional episode (odds ratio, 0.21; P = .006). Associations were also identified for specific HLA types and disease caused by the Beijing, LAM, LCC, and Quebec strains. HLA types were also associated with disease caused by strains from the Euro-American or East Asian lineages, and the frequencies of these alleles in their sympatric human populations identified potential coevolutionary events between host and pathogen. CONCLUSIONS. This is the first report of the association of human HLA types and M. tuberculosis strain genotype, highlighting that both host and pathogen genetics need to be taken into consideration when studying tuberculosis disease development.Item BDNF Val66Met and DRD2 Taq1A polymorphisms interact to influence PTSD symptom severity: A preliminary investigation in a South African population(Elsevier, 2013) Hemmings, Sian M.J.; Martin, Lindi I.; Klopper, Marisa; van der Merwe, Lize; Aitken, Lisa; de Wit, Erika; Black, Gillian F.; Hoal, Eileen G.; Walzl, Gerhard; Seedat, SorayaBACKGROUND: We evaluated the role that selected variants in serotonin transporter (5-HTT), dopamine receptor 2 (DRD2) and brain-derived neurotrophic factor (BDNF) genes play in PTSD symptom severity in an at-risk population. We also investigated the interaction between the genetic variants to determine whether these variables and the interactions between the variables influenced the severity of PTSD symptoms. METHODS: PTSD symptoms were quantitatively assessed using the Davidson Trauma Scale (DTS) in 150 participants from an at-risk South African population. All participants were genotyped for the 5-HTTLPR, DRD2 Taq1A and BDNF Val66Met polymorphisms. Gene–gene interactions were investigated using various linear models. All analyses were adjusted for age, gender, major depressive disorder diagnosis, level of resilience, level of social support and alcohol dependence. RESULTS: A significant interaction effect between DRD2 Taq1A and BDNF Val66Met variants on DTS score was observed. On the background of the BDNF Val66Val genotype, DTS score increased significantly with the addition of a DRD2 Taq1A A1 allele. However, on the BDNF Met66 allele background, the addition of an A1 allele was found to reduce total DTS score. CONCLUSIONS: This study provides preliminary evidence for an epistatic interaction between BDNF Val66Met and DRD2 Taq1A polymorphisms on the severity of PTSD symptoms, where both too little and too much dopamine can result in increased PTSD symptom severity.Item BDNF Val66Met modifies the risk of childhood trauma on obsessive-compulsive disorder(Elsevier, 2013) Hemmings, Sian Megan Joanna; Lochner, Christine; van der Merwe, Lize; Cath, Danielle C.; Seedat, Soraya; Stein, Dan J.Childhood trauma has been linked to the development of later psychopathology, including obsessive-compulsive disorder (OCD). Although evidence exists to suggest that genetic and environmental factors are involved in the aetiology of OCD, little attention has been paid to the interactions that exist between genes and environment. The aim of this study was to investigate gene-by-environment interactions between childhood trauma and the BDNF Val66Met variant in patients with OCD. Childhood trauma was assessed in 134 OCD patients and 188 controls using the Childhood Trauma Questionnaire (CTQ). Linear regression models were used for statistical analyses. Geneeenvironment interactions were estimated by including a combined genotype and CTQ score in the models as interaction terms. All analyses were adjusted for age, gender, CTQ minimisation-denial score and home language by including them in the logistic regression models as covariates. Childhood trauma, specifically emotional abuse and neglect, increased the odds of having OCD significantly (p < 0.001). Although no significant association was observed between BDNF Val66Met and the development of OCD, interaction analysis indicated that the BDNF Met-allele interacted with childhood emotional abuse to increase the risk of OCD significantly in a dose-dependent manner (p < 0.024). To our knowledge, this is one of the first studies to investigate geneeenvironment interactions in OCD, and the findings indicate the importance of collating genetic and environmental variables in future studies.Item Boys or girls? Sex preferences declared in African and South-Asian demographic surveys(Elsevier, 2023) Garenne, Michel; Stiegler, Nancy; Bouchard, Jean-PierreIn 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.Item Causes and patterns of morbidity and mortality in Afghanistan: Joint estimation of multiple causes in the neonatal period(Springer, 2014) Adegboye, Oyelola A.; Kotze, DanelleThis 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.Item Child mortality rate in Ethiopia(Tehran University of Medical Sciences, 2012) Appunni, Sathiya SusumanEthiopia’s childhood mortality has continued to decline although at a swift pace. The drop in urban childhood mortality decline, duration of breastfeeding is the principle reason for the overall decline in mortality trends in Ethiopia. Data from the Ethiopian Demographic and Health Surveys 2000 and 2005 were used. Indirect estimation of Brass and Trussell’s methods were adopted. Selected demographic and socio-economic variables were included in the analysis with statistically significant effects. Findings clearly show neonatal and post neonatal mortality decline gradually. Even though, Ethiopia’s childhood mortality rates are still high. The result shows less than 2 years birth interval have higher infant mortality rates than higher birth interval (113 deaths per 1000). The proper spacing of births allows more time for childcare to make more maternal resources available for the care of the child and mother. Therefore, further research is urgent for regional level and national level investigation.Item A comparative analysis of contraceptive use in Africa: evidence from DHS(SAGE Publications, 2016) Stiegler, Nancy; Appunni, Sathiya SusumanThe aim of this article is to show a comparative analysis of contraceptive use in areas of traditionally high fertility that have gone through profound changes. Data have been taken from the latest Demographic and Health Surveys (DHS). Logistic regression models were adopted for four selected representative countries, namely Egypt, Mali, Namibia and Niger. There were two selection criteria: data should be recent, and selected countries should have high (Egypt 57.4%; Namibia 46.4%) or low (Mali 7.5%; Niger 10.0%) contraceptive use. The probability of using contraception when a woman has had one to four children is 2.4 times higher than when they have had no children. Contraception data are always gathered at a point of time, but crosssectional data are not sufficient to understand all the mechanisms hidden behind contraceptive use. Different contraceptive behaviours need good estimation tools to develop specific family planning programmes.Item Comparative analysis of the use of professional health providers by young mothers in developing countries: A new frontier for health education(AFAHPER-SD, 2016) Kabongo, Muika; Stiegler, Nancy; Kanayo, OgujiubaChildbearing accelerates the risk of maternal and child morbidity and young mothers have a much higher risk of dying from maternal causes. Therefore, understanding the dynamics of young mothers’ use of professional health providers during pregnancy and childbirth in developing countries as well as identifying the socioeconomic factors that influence them is imperative. The paper investigates the relationship between the utilization of professional health providers and socioeconomic influence in Kenya, Ethiopia, Haiti, Bangladesh and Guyana. Both Chi-square and logistic regression models were used on the Demographic and Health Survey data set of the select countries to determine the relationship between young mothers’ characteristics and use of professional health providers. Using bivariate and multivariate analysis, socioeconomic and demographic factors were triangulated to capture the relationships between professional health providers’ utilization and young mothers. Test statistics showed that age and education had a positive, statistically significant relationship with the young mothers’ use of professional health providers for delivery in Kenya, (p=0.01<0.05) in Ethiopia (p=0.01<0.05) and in Haiti (p=0.01<0.05). The results of logistic regression also showed a positive statistical significance between the young mothers’ use of professional health providers and level of education, wealth, and place of residence (p=0.05) for the select countries. Our findings suggest that socioeconomic conditions in the selected countries influence the use of professionals for both prenatal and natal care. In order to improve maternal and child health in accordance with Sustainable Development Goals, emphasis should be placed on providing health education for young women and expanding the knowledge curriculum of professional health providers that attend to them. While recognizing that the health educator has contributions to make on both the micro and macro change levels, a case is made for moving the field of health education further in the broad direction of prenatal and natal care. This would impact positively on the socioeconomic status of women in general.Item Confidence intervals for the correlation between the gamma-ray burst peak energy and the associated supernova peak brightness(Oxford University Press, 2009) Koen, ChrisA strong correlation between the gamma-ray burster peak energy and the peak luminosity of the associated supernova was discovered by Li for four GRBs. Despite the fact that the formal significance level of the correlation is 0.3 per cent, the smallness of the data set requires careful further evaluation of the result. Subject to the assumption that the data are bivariate Gaussian, a 95 per cent confidence interval of (−0.9972, 0.02) for the correlation is derived. Using data from the literature, it is shown that the distribution of known peak GRB energies is not Gaussian if X-ray flashes are included in the sample. This leads to a proposed alternative to the bivariate Gaussian model, which entails describing the dependence between the two variables by a Gaussian copula. The copula is still characterized by a correlation coefficient. The Bayesian posterior distribution of the correlation coefficient is evaluated using a Markov chain Monte Carlo method. The mean values of the posterior distributions range from −0.33 to about zero, depending on the specifics of the supernova (SN) peak brightness distribution. The implication is that the existing data favour a modest correlation between the GRB peak energy and the SN peak brightness; confidence intervals are very wide and include zero.Item Control of airborne microbes in a poultry setting using Dioxy MP 14(FACTA-FUNDACIO ARNCO CIENCIA TECNOLOGIA AVICOLAS, 2015) Mbamalu, O; Uebel, R; Meki, BIn this study, Dioxy MP 14, a locally developed form of chlorine dioxide, was tested in a commercial chicken pen to determine its effectiveness as an airborne environmental sanitizing agent. The biocide was introduced via an overhead misting system with a variable dosing pump. The extent of airborne microbial control was determined with settle plates. Performance and mortality rate of the chickens in the experimental pen was compared to that in the control pen. Results show a decrease in airborne microbial load and a significantly higher egg productivity rate at a 5% level in the treated pen. However, no significant difference in mortality rates between the two pens was observed.Item Correcting CCD photometry of stars for seeing effects(Oxford Univeristy Press, 2009) Koen, ChrisSystematic variability in stellarmagnitudes, as derived from profile fitting to CCD images,may in some instances be due to variable seeing. It is suggested that this happens in cases where the stars are unresolved pairs, typically with sub-arcsecond separation between the components. It is shown that the fitting of suitable Generalised Additive Models to time series photometry can disentangle intrinsic stellar variability and seeing-induced brightness changes. It is possible that there will be a fixed seeing response associated with a given star which exhibits the effect: estimation of this response from several long photometric runs is demonstrated.Item Correlates of antenatal and postnatal care among tribal women in India(Kamla-Raj Enterprises, 2012) Appunni, Sathiya SusumanIt is well established that those women who undergo full antenatal care check-up and give birth in a medical institution or whose delivery is attended by trained paramedical persons promotes child survival and reduces maternal mortality. In the light of the above, an attempt is made in this paper to relate the socio-economic and demographic characteristics of the currently married Schedule Tribes’ women in eight districts of Chhatisgarh with factors associated with antenatal and postnatal care. Data for this study were taken from District Level Household Survey on Reproductive and Child Health (DLHSRCH 2002), a representative sample of 1569 Scheduled Tribes’ currently married women aged 15-44, residing in eight districts of Chhatisgarh. Adjusted effects (odds ratios) analysis has been used to find out the effects of antenatal and post-natal care on institutional delivery in Chhatisgarh. It is observed that majority of the Scheduled Tribes’ women, about 84 percent, have a low standard of living. Also, 74 per cent of the Scheduled Tribes’ women are illiterate. The finding of the adjusted effects (odds ratio) shows that giving birth in the medical institution for the Scheduled Tribes’ women who received full antenatal check up is 2.5 times higher than those women who did not receive any antenatal check-up. It suggests that majority of the currently married Scheduled Tribe women have low standard of living there is a need to improve their economic standard so that they can fulfill their basic needs.