Philosophiae Doctor - PhD (Statistics and Population Studies)
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Item Analysis and estimation of customer survival Time in subscription-based businesses(University of the Western Cape, 2008) Mohammed, Zakariya Mohammed Salih; Kotze, Danelle; Maritz, Johannes Stefan; Dept. of Statistics; Faculty of ScienceSubscription-based industries have seen a massive expansion in recent decades. In this type of industry the customer has to subscribe to be able to enjoy the service; there-fore, well-de ned start and end points of the customer relationship with the service provider are known. The length of this relationship, that is the time from subscription to service cancellation, is de ned as customer survival time. Unlike transaction-based businesses, where the emphasis is on the quality of a product and customer acquisition, subscription-based businesses focus on the customer and customer retention. A customer focus requires a new approach: managing according to customer equity (the value of a rm's customers) rather than brand equity (the value of a rm's brands). The concept of customer equity is attractive and straightforward, but the implementation and management of the customer equity approach do present some challenges. Amongst these challenges is that customer asset metric - customer lifetime value (the present value of all future pro ts generated from a customer) - depends upon assumptions about the expected survival time of the customer (Bell et al., 2002; Gupta and Lehmann, 2003). In addition, managing and valuing customers as an asset require extensive data and complex modelling. The aim of this study is to illustrate, adapt and develop methods of survival analysis in analysing and estimating customer survival time in subscription-based businesses. Two particular objectives are studied. The fi rst objective is to rede ne the existing survival analysis techniques in business terms and to discuss their uses in order to understand various issues related to the customer-fi rm relationship. The lesson to be learnt here is the ability of survival analysis techniques to extract important information on customers with regard to their loyalties, risk of cancellation of the service, and lifetime value. The ultimate outcome of this process of studying customer survival time will be to understand the dynamics and behaviour of customers with respect to their risk of cancellation, survival probability and lifetime value. The results of the estimates of customer mean survival time obtained from different nonparametric and parametric approaches; namely, the Kaplan-Meier method as well as exponential, Weibull and gamma regression models were found to vary greatly showing the importance of the assumption imposed on the distribution of the survival time. The second objective is to extrapolate the customer survival curve beyond the empirical distribution. The practical motivation for extrapolating the survival curve beyond the empirical distribution originates from two issues; that of calculating survival probabilities (retention rate) beyond the empirical data and of calculating the conditional survival probability and conditional mean survival time at a speci c point in time and for a speci c time window in the future. The survival probabilties are the main components needed to calculate customer lifetime value and thereafter customer equity. In this regard, we propose a survivor function that can be used to extrapolate the survival probabilities beyond the last observed failure time; the estimation of parameters of the newly proposed extrapolation function is based completely on the Kaplan-Meier estimate of the survival probabilities. The proposed function has shown a good mathematical accuracy. Furthermore, the standard error of the estimate of the extrapolation survival function has been derived. The function is ready to be used by business managers where the objective is to enhance customer retention and to emphasise a customer-centric approach. The extrapolation function can be applied and used beyond the customer survival time data to cover clinical trial applications. In general the survival analysis techniques were found to be valuable in understanding and managing a customer- rm relationship; yet, much still needs to be done in this area of research to make these techniques that are traditionally used in medical studies more useful and applicable in business settings.Item Assessment of the potential of hospital birth records to estimate the number of births: A case study of Germiston and Nkomazi Local Municipalities(University of the Western Cape, 2020) Nhlapo, Mosidi Sarah; Stiegler, NancyThe advantage of a well-developed health information system is the significant role played by records produced by such a system beyond recording medical history of individuals. They are the foundation for birth registrations which when fully complete is an important tool for acquiring data necessary for planning and monitoring child and maternal health in a country. This study aimed to investigate the potential of hospital birth records to estimate the number of births in the country and supplement birth registrations data. Data was abstracted from public facilities where births occur in two municipalities; Germiston in Gauteng and Nkomazi in Mpumalanga for the period 2014 to 2016. Modified version of the BORN Data Quality Framework (BORN-DQF) of the Ontario Agency for Health Protection and Promotion (2016) was used to assess the contents and quality of hospital birth records.Item Challenges of postgraduate students at the University of the Western Cape 2009 - 2013(University of the Western Cape, 2019) Lewis, Priscilla-Anne; Holtman, LornaIn South Africa, postgraduate education is a catalyst in national development and poverty alleviation that is widely acknowledged by the state and higher education institutions, such as the University of the Western Cape (UWC). Previously disadvantaged universities in South Africa were systematically moulded by apartheid planning and the prevailing social-economic-political order of the time. The structural legalised differences between historically white and historically black institutions created the key inequities between them. Unjust laws and institutionalised racism caused historical black universities (HBUs), such as the University of the Western Cape, also known as the University for the left, to lag behind with the intake of postgraduate students. Prior to 1994, students, who were fortunate enough to attend university, were mostly limited to studying towards an undergraduate degree, diploma or a certificate course, in the fields of teaching, nursing or law enforcement. The dawn of democracy opened up new possibilities; however, a major sphere of concern, was the need to speedily transform the education system, to make it inclusive for all. Systematically, institutions of higher learning focussed more on postgraduate education, as it was a stepping stone to improve enrolment growth research output, and collaborative partnerships, at national and international level. However, socio-economic factors, such as the lack of funding, were major constraints, as most postgraduate students were challenged to pay registration fees, or accommodation deposits, upon registration.Item Contraception and unmet-needs in Africa(University of the Western Cape, 2009) Stiegler, Nancy; Dept. of Statistics; Faculty of ScienceThe first objective of this study is to show if diffusion of contraception in areas of traditional high fertility has gone through profound changes. Indeed, we would like to know if contraceptive behaviours have evolved because of new fertility perceptions and also because partners now have greater freedom to make choices in a relationship. The second objective of this study is not only to highlight the levels and trends of contraception and the factors influencing their use (government policies, role of family planning, etc.) in developing countries, but also to consider the population of unmet-needs of contraception. Indeed, the level of contraceptive use depends obviously on users, but also on non-users with no needs and non-users with unsatisfied needs. The understanding of this last category of females is essential to a more accurate estimation of contraception levels, and, therefore for the estimation of fertility levels. This study analyses the contraceptive use in several developing countries in Africa and highlights the unsatisfied needs of contraception, to understand why such needs exist. To do so, we shall analyse available demographic data for thirty-five African countries by using the available Demographic and Health Surveys (DHS), from the 1980's to 2000's considering the DHS I, DHS II, DHS III and DHS IV. This great variety of surveys, seventy-nine in total, permits one to compare levels of contraception and 'unmet-needs' from country to country. The surveys also, make it possible to compare the evolution over time of specific countries or specific regions, and to subsequently comprehend the determining factors of contraceptive use or non-use.Item Determinants of health care use and mothers' preventative and curative health care practices in Burkina Faso(University of the Western Cape, 2022) Badolo, Hermann; Susuman, A SathiyaIn about two-thirds of all countries in sub-Saharan Africa, low coverage of effective interventions to prevent maternal and child deaths has been attributed to both weaknesses in the supply and demand for health services. These interventions require access to and use of health services. Conceptually, the availability, quality of health care, financial and geographical accessibility, socio-economic and demographics factors and cultural barriers are the main factors associated with health care use. These associated factors and the causes of low utilization of health services have been studied by several authors in Burkina Faso and other countries, often from the point of view of health care demand or supply.Item Determinants of youth sexual behaviours and knowledge of reproductive tract infections (RTIs) and sexually transmitted infections (STIs) in Malawi : evidenced from the Demographic Health Survey 2010(University of the Western Cape, 2015) Ningpuanyeh, Wilson Chialepeh; Susuman, Sathiya A.The sexual behaviour of youths is believed to play a role in the spread of SexuallyTransmitted Infections (STIs) and Reproductive Tract Infections (RTIs). This study examinesthe determinants of youth sexual behaviours and knowledge of reproductive tract infections (RTIs) and sexually transmitted infections (STIs) in Malawi. It explores rural/urbandifferentials in sexual behaviours using indicators such as early sexual initiation, multiplesexual partnerships, and non-use of condoms, in order to establish policy recommendationstoward improving sexual behaviour among youths. The Malawi Demographic Health Survey2010 data was used. Out of a sample of 2987 males and 9559 females aged 15-24 years,5652 females and 1405 males (condom use), 675 females and 511 males (inconsistentcondom use), 6470 females and 2026 males (multiple sexual partnerships (MSP)), and 15217females and 1405 males (early sexual debut) were filtered in the study.Chi-square and logistic regression techniques were performed to test for association betweensexual behaviour indicators and socio-demographic variables. The prevalence of non-use ofcondom was higher among catholic females (OR=1.11), lower among Muslim males (OR=0.81) and higher among CCAP females (OR=1.19). Muslim females were (OR=1.42) more likely to initiate sexual activities early, while Muslim males were (OR= 0.57) less likelyto initiate sexually activities early. Females in the central region (OR=1.51) and catholicmales (OR=1.63) were more likely to have more sexual partners.Encouraging these young people to be faithful to one uninfected partner, abstinence fromsexual activities, use condoms consistently and delay sexual initiation will help curb the spread of STIs in Malawi.Item Developing a model of school climate unique to secondary schools in South Africa: A multilevel analysis approach(University of the Western Cape, 2018) Winnaar, Lolita Desiree; Blignaut, Rénette; Zuze, LindaThe educational landscape in South Africa is unique and has also seen many changes since the dawn of democracy more than 20 years ago. The apartheid education system was marred by severe inequalities between schools and, for this reason, the democratic government post 1994 established a number of policies and interventions in an attempt to improve access, equity and quality between schools. The country has made significant advances in improving access to education. This is reflected in the Millennium Development Goals progress indicators showing that, as of 2013, almost all learners between the ages of 7 and 15 were enrolled in schools. While great strides have also been made with regard to equity, evidence shows that many schools in South Africa are still largely inequitable. Education quality, however, is an area that is still of grave concern and the matter requires much attention from educational stakeholders. International studies, such as the Trends in International Mathematics and Science Study (TIMSS) and the Progress in International Reading Literacy Study (PIRLS), use learner performance to measure the quality of the system. Such studies consistently report that South Africa is performing poorly and that large inequalities still exist between schools in the country. Improved quality is associated with effective schools and, in South Africa, only 20% of schools have been found to be functional or effective. Much of research focussed on school effectiveness, both nationally and internationally, however has been explained by factors in the school, including the appropriateness of curriculum content, infrastructure, resources in the school and teacher content knowledge. These factors have been found to be strongly correlated with effective schools.Item Differentials in unemployment duration across households in South Africa: A two-level modelling approach(University of the Western Cape, 2018) Lartey, Nathaniel; Tati, GabrielThis study aimed to examine the structural changes affecting the duration of unemployment across households in South Africa. It made use of existing datasets from the Labour Force Survey produced by Statistics South Africa, covering a period of six years (2011-2016). Relations among demographic and household variables were explored to determine how they related to unemployment duration. On the basis of the relations identified, a predictive analysis of unemployment duration was attempted using two-level modelling. The results suggest a significant difference in the duration of unemployment, according to the individual socio-demographic characteristics and the household moderating variables. More specifically, the greatest share percentage of both men and women experiencing long-term unemployment were found within the age group 25-34 years. The study also found that the percentage share of Non-White population groups experiencing longer duration of unemployment was more than for the White population group. Another variable found to have great influence on the duration of unemployment was the individual’s previous work experience. Going beyond the individual’s socio-demographic characteristics to consider household variables. It was found that unemployed workers living in households headed by a female are more vulnerable to longer unemployment duration. The study found individuals living in smaller households displaying longer unemployment duration. Also, it was found that individuals living in less endowed households (households where no one or few people were in gainful employment) were more vulnerable to experiencing longer unemployment spells. The study concluded with some recommendations for employment policy and follow-up research.Item The dynamics of modern method contraception among sexually active unmarried adolescents in Nigeria(University of the Western Cape, 2022) Ojoniyi, Olaide; Stiegler, NancyIt is just stating the obvious to aver that young people in all regions are reaching puberty earlier and are habitually engaging in sexual activity at a younger age, and thereafter, marrying later. As a result, they are sexually exposed for a longer time before marriage than has historically been the case, and as such, are at higher risk of unintended pregnancy and sexually transmitted infections. Needless to say, nonmarital sexual activity is increasing among adolescents. However, less than half of those who want to avoid pregnancy are using a modern method of contraception.Item Estimating household vulnerability to poverty at the municipality level in South Africa using the cluster analysis approach(University of the Western Cape, 2023) Ahmed Abdelkarim Eldud Omer, Eldud; Tati, Gabriel; Stiegler , NancyItem Female migration and housing in South Africa: evidence from the 2007 community survey(University of the Western Cape, 2013) Nsengiyumva, Philomene; Tati, GabrielThroughout the world, growing evidence suggests an increase of female migrants in migration streams. In the context of South Africa, women are not exempted from migration mechanisms. This new migration phenomenon is observed to influence housing accessibility among female migrants in the areas of destinations specifically in metropolitan and non-metropolitan areas of South Africa. Yet, little is known about the forms of housing tenure female migrants use to acquire a place to live in. The methods of housing acquisition of female migrants are still imperfectly documented. Moreover, it is not clear of how housing tenure differs among female migrants between metropolitan and non-metropolitan areas. Factors determining housing tenure and at what extent those factors are selective towards women in the places of destination are not properly elaborated in the existing body of knowledge. The aim of this research is to highlight the relationship between female migration and housing acquisition in South Africa by specifically looking at household headship in a gender perspective, and how housing acquisition differ between metropolitan and non-metropolitan areas of South Africa. It is assumed that inasmuch as migration is selective, so is a really differentiated selectivity of such places as metropolises and non-metropolises. This research makes use of the 2007 Community Survey secondary data derived from Statistics South Africa. The data analysis was carried out, first, by means of univariate analysis, cross-tabulation, and Chi-square statistical test for association. Logistic regression analysis was used in order to identify the determining factors of housing tenure among female migrants. The two groups of female migrants were considered namely: female migrants heading households and those who were not heading households. The units of analysis were metropolitan and non-metropolitan areas. This research focuses on internal female migration and housing in South Africa by examining different socio-demographic, socioeconomic, migratory, households, and housing attributes, by taking into account variables such as age, population group, marital status, level of education, just to name the few. By bringing together female migrants characteristics, migratory characteristics; and housing characteristics, the study found that female migrants heading households living in metropolitan areas are more likely to stay in rented dwellings, while those who were living in areas outside metropolitan (non-metropolitan areas) were highly represented in owned and fully paid dwellings. This study found further that, besides duration of residence, housing structure type, especially the availability of standalone housing type increases the likelihood of staying in owned and fully paid housing. This study concludes that, this new female migration stream creates more tension and pressure on housing provision in metropolitan areas in relation to non-metropolitan areas. Thus, policy makers should be aware of female migration and its impact in the housing sector in order to plan accordingly.Item A forgotten diaspora : forced Indian Migration to the Cape Colony, 1658 to 1834(University of the Western Cape, 2015) Rama, Parbavati; Shell, Robert C. H.; Stiegler, NancyThis thesis aims to explore Indian forced migration to the Cape Colony from 1658 to 1834. The forgotten diaspora‘ of its title refers to the first Indians who had come to the shores of South Africa, long before the arrival—between 1860 and 1911—of the indentured Indians. This diaspora has been forgotten, partially because these migrants came as slaves. The author uses data extracted from the newly transcribed Master of the Orphan Chamber (MOOC) series and slave transfers which are housed in the Western Cape Provincial Archives and Records Service (WCARS). The Cape colonial data is considered among the best in the world. Earlier historians such as Victor de Kock, Anna Böeseken, Frank Bradlow and Margaret Cairns, have made us aware of their existence primarily through Transportenkennis and Schepenkennis (transport and shipping information) documents in the Deeds Registry. Not nearly enough, however, is known about these Indian slaves, especially about those who arrived between 1731 and 1834. These lacunae include the number of arrivals; their sex ratios; ages and origins; and the circumstances under which they came. This thesis aims to construct a census of Indian slaves brought to the Cape from 1658 to 1834—along the lines of Philip Curtin's aggregated census of the Trans- Atlantic slave trade, but based on individual case level data coded directly from primary sources. This is the first time the size of the creole population born at the Cape will be established.Item Fostering collaboration amongst business intelligence, business decision makers and statisticians for the optimal use of big data in marketing strategies(University of the Western Cape, 2019) De Koker, Louise; Tati, GabrielThe aim of this study was to propose a model of collaboration adaptable for the optimal use of big data in an organisational environment. There is a paucity of knowledge on such collaboration and the research addressed this gap. More specifically, the research attempted to establish whether leadership, trust and knowledge sharing influence collaboration among the stakeholders identified at large organisations. The conceptual framework underlying this research was informed by collaboration theory and organisational theory. It was assumed that effective collaboration in the optimal use of big data possibly is associated with leadership, knowledge sharing and trust. These concepts were scientifically hypothesised to determine whether such associations exist within the context of big data. The study used a mixed methods approach, combining a qualitative with a quantitative study. The qualitative study was in the form of in-depth interviews with senior managers from different business units at a retail organisation in Cape Town. The quantitative study was an online survey conducted with senior marketing personnel at JSE-listed companies from various industries in Cape Town. A triangulation methodology was adopted, with additional in-depth interviews of big data and analytics experts from both South Africa and abroad, to strengthen the research. The findings of the research indicate the changing role of the statistician in the era of big data and the new discipline of data science. They also confirm the importance of leadership, trust and knowledge sharing in ensuring effective collaboration. Of the three hypotheses tested, two were confirmed. Collaboration has been applied in many areas. Unexpected findings of the research were the role the chief data officer plays in fostering collaboration among stakeholders in the optimal use of big data in marketing strategies, as well as the importance of organisational structure and culture in effective collaboration in the context of big data and data science in large organisations. The research has contributed to knowledge by extending the theory of collaboration to the domain of big data in the organisational context, with the proposal of an integrated model of collaboration in the context of big data. This model was grounded in the data collected from various sources, establishing the crucial new role of the chief data officer as part of the executive leadership and main facilitator of collaboration in the organisation. Collaboration among the specified stakeholders, led by the chief data officer, occurs both horizontally with peers and vertically with specialists at different levels within the organisation in the proposed model. The application of such a model of collaboration should facilitate the successful outcome of the collaborative efforts in data science in the form of financial benefits to the organisation through the optimal use of big data.Item A framework for evaluating an introductory statistics programme at the University of the Western Cape(University of the Western Cape, 2009) Makapela, Nomawabo; Kotze, Danelle; Dept. of Statistics; Faculty of ScienceThere have been calls both from the government and private sector for Higher Education institutions to introduce programmes that produce employable graduates whilst at the same time contributing to the growing economy of the country by addressing the skills shortage. Transformation and intervention committees have since been introduced to follow the extent to which the challenges are being addressed (DOE, 1996; 1997; Luescher and Symes, 2003; Forbes, 2007). Amongst the list of issues that needed urgent address were the skills shortage and underperformance of students particularly university entering students (Daniels, 2007; De Klerk, 2006; Cooper, 2001). Research particularly in the South African context, has revealed that contributing to the underperformance of university entering students and shortage of skills are: the legacy of apartheid (forcing certain racial groups to focus on selected areas such as teaching and nursing), the schooling system (resulting in university entering students to struggle), the home language and academic language. Barrell (1998), places stress on language as a contributing factor towards the performance of students. Although not much research has been done on skills shortage, most of the areas with skills shortage require Mathematics, either on a minimum or comprehensive scale. Students who have a strong Mathematics background have proved to perform better compared to students who have a limited or no Mathematics background at all in Grade 12 (Hahn, 1988; Conners, McCown & Roskos-Ewoldsen, 1998; Nolan, 2002).The department of Statistics offers an Introductory Statistics (IS) course at first year level. Resources available to enhance student learning include: a problem-solving component with web-based tutorials and students attending lectures three hours per week. The course material and all the necessary information regarding the course including teach yourself problems, useful web-sites and links students can make use of, are all stored under the Knowledge- Environment for Web-based learning (KEWL). Despite all the available information, the students were not performing well and they were not interested in the course. The department regards statistical numeracy as a life skill. The desire of the department is to break down the fear of Statistics and to bring about a perspective change in students' mindsets. The study was part of a contribution to ensuring that the department has the best first year students in Statistics in the Western Cape achieving a success rate comparable to the national norm.Item Handling heteroskedasticity in the linear regression model(University of the Western Cape, 2022) Farrar, Thomas; Blignaut, RénetteThis research project delves into the problem of heteroskedasticity in the linear regression model. Having defined the problem and its consequences for estimation and inference, a comprehensive literature review of existing methods for diagnosing and correcting for heteroskedasticity is undertaken, with special emphasis on heteroskedasticity tests. New theory on the statistical properties of the Ordinary Least Squares residuals is developed, leading to new models for estimating linear regression error variances. The most important of these models is the Auxiliary Linear Variance Model, which is further classified into sub-types (e.g., clustering, linear, penalised polynomial, spline). Model fitting techniques are discussed, which reduce to quadratic programming problems. An Auxiliary Nonlinear Variance Model is also developed, which can be fitted using a maximum quasi-likelihood method. Techniques for tuning of model hyperparameters and feature selection are discussed. Bootstrap methods of obtaining interval estimates for error variances are also proposed. A new heteroskedasticity test is constructed based on the auxiliary linear variance model. To make existing and new methods of handling heteroskedasticity more accessible to the practitioner, a new package called skedastic has been developed for R statistical software. Its functionality is described in detail.Item Health inequalities of children in sub-Saharan Africa from 1990 to 2010 : comparative analysis using data from Health and Demographic Surveys(University of the Western Cape, 2016) Bado, Aristide Romaric; Susuman, Sathiya A.This study is based on the assumption that the under-five mortality rate, in recent decades, has declined, particularly in developing countries. However, all the social strata across many countries do not seem to benefit from this reduction of mortality - and mortality remains abnormally high among children especially those from underprivileged social strata. This research is, therefore, a holistic approach to analyse and quantify the inequalities of health among children under five in sub-Saharan Africa over the last two decades (1990-2010). The research sought to investigate the trend and determinants of health inequalities of under-five years (mortality and morbidity) in sub-Saharan Africa (SSA) from 1990 to 2010. An essential point has been devoted to the decomposition of effects and analysis of the contribution of the factors explaining these inequalities. The data used in the study come from Demographic and Heath Surveys (DHS) done between 1990 and 2015 in sub-Saharan Africa countries. In order to analyse the inequalities in trends of mortality and morbidity of children, different selected countries that have conducted at least three DHS during the 1990-2010 period. Several statistical methods were used for data analysis. There were four chapters which is prepared with an article style. For the first paper titled "Decomposing Inequalities in Under- Five Mortality in Selected African Countries", concentration index (CI) and Generalised Linear Model (GLM) with a logit link were used to analyse and measure under 5 mortality inequalities and the associated factors. This paper has been published in the Iranian Journal of Public Health. For the second paper titled "Determinants of Under-Five Mortality in Burkina Faso: A Concentration Dimension". The study used logistics regression and Oaxaca-Blinder decomposition method for the binary outcome to analyse data was involved. For data analysis of the third paper titled "Women Education, Health Inequalities in Under-Five Mortality in sub-Saharan Africa, 1990 – 2013", logistic regression and Bius's decomposition method were used to examine the effect of mother's education level on childhood mortality. In the fourth paper titled "Trends and Risk Factors for Childhood Diarrheal in sub-Saharan Countries (1990-2010): Assessing the Neighbourhood Inequalities", a multilevel logistic regression modelling was used to determine the fixed and random effects of the risk factors associated with the diarrheal morbidity. The work carried out during this on-going thesis helps to understand the magnitude of inequalities in under-five mortality in sub-Saharan countries. The findings showed that the contributing factors of inequalities of child mortality were birth order, maternal age, parity and household size. With regards to the relationship between mother's education level and inequalities in mortality of children under-five in sub-Saharan Africa, findings showed that children of mothers who did not attend school have a higher rate of death compared to those who had been to school. However, we have observed that the inequalities have narrowed over time. The results showed the risk factors of diarrheal morbidity varied from one country to another, but the main factors included: child's age, the size of the child at birth, the quality of the main floor material, mother's education and her occupation, type of toilet, and place of residence. In conclusion, the results of this study show that inequalities in under-five mortality are still important among different social strata in sub-Saharan Africa countries. It is then urgent to take actions to save the lives of children in disadvantaged social strata.Item Imputation techniques for non-ordered categorical missing data(University of the Western Cape, 2016) Karangwa, Innocent; Kotze, Danelle; Blignaut, RenetteMissing data are common in survey data sets. Enrolled subjects do not often have data recorded for all variables of interest. The inappropriate handling of missing data may lead to bias in the estimates and incorrect inferences. Therefore, special attention is needed when analysing incomplete data. The multivariate normal imputation (MVNI) and the multiple imputation by chained equations (MICE) have emerged as the best techniques to impute or fills in missing data. The former assumes a normal distribution of the variables in the imputation model, but can also handle missing data whose distributions are not normal. The latter fills in missing values taking into account the distributional form of the variables to be imputed. The aim of this study was to determine the performance of these methods when data are missing at random (MAR) or completely at random (MCAR) on unordered or nominal categorical variables treated as predictors or response variables in the regression models. Both dichotomous and polytomous variables were considered in the analysis. The baseline data used was the 2007 Demographic and Health Survey (DHS) from the Democratic Republic of Congo. The analysis model of interest was the logistic regression model of the woman’s contraceptive method use status on her marital status, controlling or not for other covariates (continuous, nominal and ordinal). Based on the data set with missing values, data sets with missing at random and missing completely at random observations on either the covariates or response variables measured on nominal scale were first simulated, and then used for imputation purposes. Under MVNI method, unordered categorical variables were first dichotomised, and then K − 1 (where K is the number of levels of the categorical variable of interest) dichotomised variables were included in the imputation model, leaving the other category as a reference. These variables were imputed as continuous variables using a linear regression model. Imputation with MICE considered the distributional form of each variable to be imputed. That is, imputations were drawn using binary and multinomial logistic regressions for dichotomous and polytomous variables respectively. The performance of these methods was evaluated in terms of bias and standard errors in regression coefficients that were estimated to determine the association between the woman’s contraceptive methods use status and her marital status, controlling or not for other types of variables. The analysis was done assuming that the sample was not weighted fi then the sample weight was taken into account to assess whether the sample design would affect the performance of the multiple imputation methods of interest, namely MVNI and MICE. As expected, the results showed that for all the models, MVNI and MICE produced less biased smaller standard errors than the case deletion (CD) method, which discards items with missing values from the analysis. Moreover, it was found that when data were missing (MCAR or MAR) on the nominal variables that were treated as predictors in the regression model, MVNI reduced bias in the regression coefficients and standard errors compared to MICE, for both unweighted and weighted data sets. On the other hand, the results indicated that MICE outperforms MVNI when data were missing on the response variables, either the binary or polytomous. Furthermore, it was noted that the sample design (sample weights), the rates of missingness and the missing data mechanisms (MCAR or MAR) did not affect the behaviour of the multiple imputation methods that were considered in this study. Thus, based on these results, it can be concluded that when missing values are present on the outcome variables measured on a nominal scale in regression models, the distributional form of the variable with missing values should be taken into account. When these variables are used as predictors (with missing observations), the parametric imputation approach (MVNI) would be a better option than MICE.Item Inequalities in the use of maternal and reproductive health services in Sierra Leone(University of the Western Cape, 2019) Tsawe, Mluleki; Susuman, SathiyaThis thesis extends the literature on the trends and magnitude of health inequalities in the area of maternal and reproductive health services in Sierra Leone, and particular across sub-Saharan Africa. It attempted to provide a good understanding of, not only the determinants of maternal and reproductive healthcare use, but also factors that enable health inequalities to exist in Sierra Leone. This is an appropriate topic in population health studies as it aims to address important questions on the research agenda in the context of sub-Saharan Africa, particularly in a country with poor health outcomes such as Sierra Leone. A proper understanding of not only the coverage rates of population health outcomes but also the extent of health inequalities as well as the factors that contribute to these inequalities is crucial for any government. The thesis applied various techniques in the analysis of DHS data (from 2008 and 2013 rounds) in an attempt to answer the research questions.Item Influence of data accuracy and non-use of quality information on reproductive health: a comparative study of Nigeria and South Africa(University of the Western Cape, 2023) Oyekola, Adetooke Bukola; Sathiyasusuman, Appunni; Appunni, SathiyasusumanIn healthcare settings, information systems play a critical role in providing safe, timely, and effective healthcare services. Decision-making on medical supplies, healthcare providers, service delivery, finance, and governance all depend on access to health information. To improve overall health services and processes, these information systems manage data collection, processing, storage, retrieval, and utilisation. The effectiveness of health systems depends on effective administration and data quality. Irrespective of the significance of health information systems, many low- and middle-income nations, such as South Africa and Nigeria, continue to encounter challenges with data accuracy and the use of high-quality information. Inaccurate data can lead to misinformed policy decisions and resource allocation, hindering efforts to improve reproductive health outcomes. Problems such as incomplete, outdated, unreported data, poor integration, and underutilisation of technology affect data quality and completeness. Data quality impacts decision-making, performance, and the ability to achieve national and international health goals. Government involvement and suitable policies are crucial for addressing these challenges and improving the effectiveness of health information systems.Item An investigation into the health and well-being of older people in South Africa.(University of the Western Cape, 2014) Chirinda, Witness; Susuman, Sathiya A.Populations are rapidly growing older across the globe. In South Africa, life expectancy has been on the increase over the past decade, and the proportion of older people is projected to increase dramatically over the coming years. Whilst this is a remarkable achievement, it does not mean that additional years of life will be healthy. To this end, the question being asked by researchers and policy makers is whether people are living longer and healthier lives? In order to answer this important question, health expectancies have been developed which combine morbidity and mortality data into a single index that measures population health. The health expectancies have become standard measures of population health across first world countries. Unfortunately, there is little awareness about their use in developing countries, including South Africa. The aim of this study was to estimate health expectancies based on various objective and subjective measures, in order to give a first comprehensive analysis of the health and wellbeing of older people in South Africa. The data were drawn from two nationally representative surveys namely; the WHO-Study on Global Ageing and Adult Health (SAGE) and the South African National HIV Incidence, Prevalence, Behaviour and Communication Survey (SABSSM) surveys. The results are presented in the form of five manuscripts each submitted for publication. The first manuscript estimates sexually active life expectancies and factors associated with sexual activity. The results show that older people are gaining more years of sexual activity. HIV in older women and chronic conditions in older men reduced odds of sexual activity. The second manuscript found that there was both absolute and relative compression of morbidity in older people between 2005 and 2012, based on self-rated health measure. The third manuscript estimates happy life expectancy and examines factors associated with happiness in older people. Happy life expectancy was greater for men than women, and wealth status was the strongest predictor of happiness. In the fourth manuscript, subjective and objective measures were used to estimate health expectancies. The former showed a more positive outlook compared to the latter. Gender differentials were evident in that although women live longer than men, they spent a greater part of their lifetime in poorer health than men. The fifth manuscript goes a crucial step further, to estimate the contribution of specific diseases to disability. This is important for policymakers as this identifies entry points of interventions aimed at reducing the onset and burden of disability in the elderly population. The most contributors of disability were musculoskeletal and cardiovascular diseases. The thesis concludes that the health of older people is complex and multidimensional, and therefore requires several measures to give a comprehensive analysis. When measured using subjective measures, it can be concluded that the health of older people has been improving. However, a different conclusion could be reached, if objective measures are used. It is important to continue to monitor the health status of older people, and make appropriate interventions in order to improve their health, wellbeing and quality of life.