Browsing by Department "Centre for Actuarial Research (CARE)"
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- ItemOpen AccessAn investigation into the progression of premarital fertility since the onset of Zimbabwe's fertility transition(2021) Ngwenya, Chantelle Linda; Moultrie, ThomasPremarital fertility, that is, childbearing before first marriage, is an important yet under researched demographic topic in sub-Saharan Africa. In Zimbabwe, the distinction by marital status in fertility research is hardly drawn. Hence, a gap exists in the knowledge of premarital fertility levels. This research aims to investigate levels of, and factors associated with, premarital fertility since the onset of Zimbabwe's fertility transition in the mid-1980s. The research employed direct fertility estimation techniques to effectively compare premarital, marital, and overall fertility trends between 1988 and 2015. Cox proportional-hazards regression and forest plot analyses were then used to explain changes in factors associated with the timing of premarital first births over the same period. Data quality assessments were carried out using the method of cohortperiod fertility rates to provide explanations for any erratic results. The results showed that premarital fertility was constant and moderate, with an average of 0.7 children per woman, between 1988 and 2015. While most premarital first births consistently occurred to younger women, from 2005 onwards, they increased among women aged above 24 years and decreased among adolescents. An increase in age, commencing sexual activity after adolescence, and improved socio-economic status including level of education decreased the relative risk of having a premarital first birth. However, delaying marriage past young womanhood, history of contraceptive use, Ndebele ethnicity, and residence in regions other than Manicaland and Masvingo, especially Ndebele dominated regions, increased the same risk by 465.0%, 45.5%, 136.0% and up to 135.0% respectively. The stagnation of premarital fertility between 1988 and 2015 while both marital and overall fertility first declined and then stalled indicates that there is insufficient evidence to suggest that premarital fertility had contributed to the stall of fertility decline in Zimbabwe from the mid-1990s. The timing of premarital first births since the start of the fertility transition in the 1980s has had a strong ethnic and cultural bias. Due to evidence of the effect of migrancy and tourism on premarital fertility in border and tourism towns, an extension into the theory of migrant premarital sexual behaviour to detail the risk of premarital fertility among border town residents who interact with but are neither migrants nor tourists is recommended.
- ItemOpen AccessAn investigation of the mortality of South African assured lives(2005) O'Malley, B R; Dorrington, R E; Jurisich, S C; Valentini, J A; Cohen, T M; Ross, B JThis paper outlines the findings of an investigation of the mortality of South African assured lives, covering the period 1995 to 1998. The investigation was carried out by the Continuous Statistical Investigations (CSI) Committee of the Actuarial Society of South Africa (ASSA). Some of the major findings of the investigation were worsening mortality below age 50, general improvements in mortality above age 50, substantial differences in mortality between the different socio-economic classes and signs of anti-selection below age 50, especially in the better socioeconomic classes.
- ItemOpen AccessAnalysis of the projected parity progression ratio method using two successive censuses(2013) Mutakwa, Darlington; Moultrie, TomThe objective of this study is to assess how well the projected parity progression ratio method works when applied to two successive censuses or Demographic Health Surveys. Four countries, namely Malawi, Zimbabwe, Cambodia and Panama, each with two recent censuses which are ten years apart, are used. Each of the census and survey used is taken through a data quality assessment process to check for inconsistencies. Using age-order specific fertility rates derived from births in the past year, parity progression ratios are projected to the next census.
- ItemOpen AccessAn assessment of the feasibility of using administrative data in producing mid-year population estimates for South Africa(2015) Hlabano, Mbongeni Charles; Dorrington, RobThe production of mid-year population estimates is an important undertaking which informs various stakeholders in policy formation and decision making. For instance, national governments use mid-year estimates to allocate seats in parliament to various constituents and public health sectors use them to monitor and improve service delivery. Mid-year population estimates undoubtedly serve very important purposes that affect lives of many people. As such, national statistical offices in various countries are given the mandate to produce annual mid-year population estimates. Statistics South Africa (Stats SA) assumes the function of producing and publishing official mid-year estimates of the population in South Africa. Stats SA produces its mid-year estimates using DemProj, population projection software which is part of the SPECTRUM suite of policy models developed by the Futures Institute. However, Stats SA does not publish full details of its adaptation of DemProj when producing its mid-year estimates as it regards this as proprietary. Concerns have been raised about the accuracy of the official mid-year estimates in terms of age distribution, particularly for ages below 40 last birthday in 2011 (e.g. Dorrington 2013). As such, this research critically analyses the method used by Stats SA to produce mid-year estimates and assesses the feasibility of using administrative data to produce mid-year estimates for South Africa. The base population is adapted from the 2001 census population. Birth and death registration data are used in a cohort component approach to produce alternative mid-year estimates for South Africa for the years 2002-2011. Prior to using these data, they are adjusted for incompleteness of registration. Levels of completeness of birth and death registration are estimated by extrapolating earlier estimates of completeness from various researchers. The mid-year estimates obtained are compared with those published by Stats SA in order to assess the relative quality of the two series of mid-year estimates. The mid-year estimates for 2011 are also compared with the mid-year population estimated from the 2011 census. These comparisons help identify the mismatches to the census and their possible causes and as such, these may lead to improved population estimates in the future, and a viable alternative method to that currently being used by Stats SA.
- ItemOpen AccessAssessment of the IGME methods of estimating infant mortality rate and neonatal mortality rate from under-five mortality rate in countries affected by HIV(2012) Ayalew, Kassahun Abere; Dorrington, RobThis study assesses the UN Inter-agency Group for Child Mortality Estimation (IGME) methods of estimating the infant and neonatal mortality rates from the under-five mortality rates in countries affected by HIV/AIDS. It uses Botswana, Malawi and South Africa as case studies. The assessment is made by comparing the IGME results with estimates from projection models and empirical results computed from survey data and vital statistics data corrected for the level of incompleteness for the countries included in the study. In addition, relevant literature is reviewed in order to determine the reasonableness and impact (on the results produced) of the assumptions made by the method.
- ItemOpen AccessAssessment of the robustness of recent births in estimating infant mortality using multi-country Demographic Health Survey data(2014) Munjoma, Malvern; Moultrie, Tom; Dorrington, RobThis dissertation investigates the robustness of recent births in estimating infant mortality rates from the proportion of deaths observed among births reported in a 24month period. The Blacker Brass technique is applied to all births reported in the 24month period and to most recent births in the 24 month period. The study uses birth history data from 76 Demographic and Health Surveys conducted in 16 countries across the developing world between 1986 and 2011. All births (and the deaths of those births) occurring in five 2-year periods before each survey were extracted to obtain five estimates of infant mortality using the Blacker-Brass and direct estimation methods from each dataset. This allows trends in infant mortality for the 10-year period before the survey to be compared and relative errors to be calculated. The results showed a decline in infant mortality in most datasets and are consistent with the United Nations and the World Health Organisation 2013 estimates. The relative errors did not indicate any systematic bias of the Blacker-Brass method applied to all births; however, further investigations showed that the method underestimated infant mortality in the period closest to the survey date in most datasets. Furthermore, the relative errors were positively correlated with the directly estimated level of infant mortality. There were, however, no significant differences in the relative errors across countries.
- ItemOpen AccessAvoiding data mining bias when testing technical analysis strategies - a methodological study(2020) Douglas, Rowan; Gilbert, Evan; Maritz, ErichWhen seeking to identify a profitable technical analysis (TA) strategy, a na¨ıve investigation will compare a large number of possible strategies using the same set of historical market data. This process can give rise to a significant data mining bias, which can cause spurious results. There are various methods which account for this bias, with each one providing a different set of advantages and disadvantages. This dissertation compares three of these methods, the step wise Superior Predictive Ability (step-SPA) method of P.-H. Hsu, Y.-C. Hsu and Kuan (2010), the False Discovery Rate (FDR) method of Benjamini and Hochberg (1995) and the Monte Carlo Permutations (MCP) method of Masters (2006). The MCP method is also extended, using a step wise algorithm, to allow it to identify multiple profitable strategies. The results of the comparison show that while both the FDR and extended MCP methods can be useful under certain circumstances, the stepSPA method is ultimately the most robust, making it the best choice in spite of its significant computational requirements and stricter set of assumptions.
- ItemOpen AccessBirth spacing and child mortality in Mozambique : evidence from two demographic and health surveys(2008) Gonçalves Sandra Dzidzai; Moultrie, TomThis research examines child mortality risk associated with short preceding birth intervals in Mozambique in quinquennial periods between 1978 to 1998 using data from the 1997 and 2003 DHS. A log rate model for piecewise constant rates is applied. The piecewise hazard function assumes a constant hazard rate of child mortality in each 6 month category of the preceding birth interval. The negative binomial regression model is applied to account for the overdispersion present in the Poisson model.
- ItemOpen AccessChild and adult mortality in Zimbabwe, 1980-2005(2011) Marera, Double-Hugh; Dorrington, RobThis research applies direct and indirect methods to data from censuses and Demographic and Health Surveys to derive empirical estimates of the level and trends of child and adult mortality in Zimbabwe from 1980 to 2005.
- ItemOpen AccessContraceptive histories: a comparative analysis of switching behaviour in five East African countries(2019) Kisaakye, Peter; Moultrie, ThomasSince the inception of family planning programmes in developing countries in the 1960s, crosssectional data show remarkable progress in the adoption of modern methods of contraception. Despite the positive contribution contraception plays in preventing unwanted pregnancies, sexually active women from sub-Saharan Africa continue to grapple with unintended pregnancies, which in some instances, results in unsafe induced abortion, with its attendant risks to maternal health. This thesis uses the most recent (as of January 2017) reproductive calendar data from the Demographic and Health Survey (DHS) programme from five East African countries; Ethiopia (2011), Kenya (2014), Rwanda (2014/15), Tanzania (2015/16), and Uganda (2011), to examine how women use contraception over time. The reproductive calendar data that are collected retrospectively provides a better mechanism to understand the trajectory of how women adopt, and immediately switch, contraception than if current-status data were utilised. Three important findings emerge from the analyses: First, contraceptive use being the most important driver of fertility decline, the slow fertility transition that is evident in the five countries can be largely attributable to limited immediate switching of contraception following discontinuation. Despite this universal observation, the key indicators of immediate switching are largely country-specific, which suggests differences in the way family planning programmes are implemented in these countries. Second, all five countries follow a similar pattern of adopting modern contraception – where the majority of users adopt short-term methods compared to long-acting reversible contraceptives (LARCs). However, the duration of use of short-term methods is observed to be shorter compared to LARCs, implying that LARCs facilitate contraceptive continuation. Last, the analysis of current-status data point to improvements in quality of contraceptive provision, and availability – facilitating increased adoption of modern contraception. However, the results indicate that method information exchange is a key predictor of contraceptive use in all countries, with users of LARCs receiving more information than users of short-term methods. Although family planning programmes have made big strides in recruiting new users, this thesis argues that unintended pregnancy, which often leads to a slow fertility transition, can be prevented once family planning programmes emphasise the benefits of immediately switching, or consistent use of contraception among existing users. Sub-optimal switching of contraception among already existing users is likely to attenuate fertility transition.
- ItemOpen AccessDefining a sub-Saharan fertility pattern and a standard for use with the relational Gompertz model(2009) Van Gijsen, Rienier; Moultrie, TomThe relational Gompertz model is often used to obtain fertility estimates for sub-Saharan Africa populations. This indirect estimation technique is dependent on a fertility standard - the Booth standard. This standard was developed in 1979 using a selection of 33 Coale-Trussell schedules congruent with high fertility patterns. However, evidence from 61 Demographic and Health Surveys of sub-Saharan countries shows that fertility has decreased to levels that were considered medium fertility at the time the standard was developed. This raises concerns about the continued relevance of the (high fertility) Booth standard. In particular, the standard would appear to consistently underestimate fertility among African women aged 45-49.
- ItemOpen AccessThe determinants of contraceptive use in Zambia(2011) Fushayi, Nelly; Moultrie, TomThe contraceptive prevalence rate in Zambia is high, while fertility decline is very slow. From 1992 to 2007, the contraceptive prevalence rate (CPR) increased from 8.9 per cent in 1992 to 32.7 per cent in 2007; while total fertility rate (TFR) fluctuated between 6.5 and 6.2. The study uses three Zambian Demographic and Health Survey (DHS) data sets for 1996, 2001-2 and 2007 and applies multivariate logistic regression techniques to identify factors affecting the use and choice of modern contraceptives by Zambian women. The study seeks to identify how contraceptive use in Zambia influences fertility and why both contraceptive use and fertility are high. In our results, place of residence (urban/rural), age, education, number of living children and formal employment were identified as factors that are significantly related to use of modern contraceptives.
- ItemOpen AccessDoes the 2008 HSRC survey indicate a turning tide of HIV prevalence in children, teenagers and the youth?(2009) Dorrington, RobRecently the HSRC released its report on the results of its third and most recent household prevalence survey. The main conclusion of their analysis is that “some solid progress has been made in the fight against the disease in the past few years, especially among teenagers and children”. In particular the authors conclude: • that HIV prevalence at national level has decreased amongst children aged 2-14, from 5.6% in 2002 to 2.5% in 2008, • that there was a substantial decrease in incidence in 2008 in comparison to 2002 and 2005, especially for the single age groups 15, 16, 17, 18, and 19, • that HIV prevalence has decreased amongst youth aged 15-24 from 10.3% in 2005 to 8.6% in 2008, and • that HIV prevalence among adults aged 15-49 has declined between 2002 and 2008 in the Western Cape, Gauteng, Northern Cape and the Free State, “with the largest decline of 7.9 (sic) percentage points in the Western Cape”. How reliable are the results from the survey and how reasonable are these conclusions?
- ItemOpen AccessEconomic evaluation of health care : cautions for the developing country context(2002) Skordis, Jolene; Nattrass, NicoliHealth economics has expanded enormously as a sub-discipline in the last four decades, drawing primarily on the theoretical foundations of welfare economics. The toolkit for the economic evaluation of health care now extends from the humble cost-minimisation exercise, through cost effectiveness measures, to the more complex cost utility or cost benefit models. These methodologies have differing strengths and drawbacks. This paper evaluates those attributes on both the practical and theoretical dimensions. On the practical dimension: The developing country context differs from the wealthier country context in a number of ways. This paper considers the differences in resource constraints and the differences in health priorities and asks to what extent the methodology is able to accommodate these variations. On the theoretical dimension: Few health care evaluations are conducted in a Pareto Optimal world. This paper considers the extent to which the welfare economic foundations of a methodology are successfully imported into its construction, and then how that foundation translates into its practical application.
- ItemOpen AccessThe effect of HIV on the orphanhood method of estimating adult female mortality(2009) Kramer, Stephen; Dorrington, RobThe orphanhood method of estimating adult mortality is widely used in developing countries. The method is subject to a number of assumptions, some of which are violated when a generalized high-prevalence HIV epidemic is present. Non-independence of the mortality of children and mothers, relationships between HIV infection and fertility, and changes in age-specific mortality result in biases that affect the accuracy of the method. An earlier study has examined some of these sources of error, and proposed adjustments to enable continued use of the method. This earlier research, however, uses data from populations with lower HIV prevalence rates than are currently being experienced in much of southern Africa, and is based on specific assumptions about HIV and its effects on mortality and fertility. The effects of HIV on the method are investigated in this research using mathematical modelling of the effects on Black South African females - a population with high HIV prevalence. More is now known about HIV and its effects on mortality and fertility, and these effects are explicitly reflected in the ASSA2002 model which provides much of the data for this research. The research compares the simulated survival of various cohorts of women: those aged 25 in a certain year, women (with an age profile identical to that of mothers), mothers, and mothers as reported by their children. In this way the various sources of error are explicitly identified and the errors quantified. The timing, magnitude, and combined effects of the errors are studied in relation to the emergence and spread of HIV, indicating when the errors might be expected to be large enough to invalidate the method. Errors that bias the outcomes of the orphanhood method take a number of years to develop after HIV starts spreading. Substantial biases in reported survival emerge between 20 and 35 years after the start of an HIV epidemic, in a high prevalence setting. These errors are reduced by the use of antiretroviral and prevention of mother-to-child transmission, but biases remain large enough to invalidate outcomes when the unadjusted method is applied in most southern African countries. An adjusted method has been proposed which substantially reduces error, except when adjusting survival reported by the two youngest age groups. This adjusted method can be applied, but further research to identify revised adjustments would further improve the accuracy of the method.
- ItemOpen AccessThe effect of HIV/AIDS on the own child-method of estimating child mortality : Lesotho and Zimbabwe(2011) Musariri, Herbert; Dorrington, RobThis study evaluates the overall impact of the bias due to HIV/AIDS on the own-child method of estimating child mortality, and the contribution of the various components to the overall bias. Indirect estimates of child mortality are calculated by applying the own-child method to the 2009 Lesotho Demographic and Health Survey (LDHS) and the 2005-6 Zimbabwe DHS. In the process, the potential of the software, MATCHTAB, to link successfully surviving children to their biological mothers is demonstrated using the 2006 Lesotho census data. To evaluate the impact of HIV/AIDS on the own-child method, the target estimates of child mortality for Lesotho and Zimbabwe are also developed by adjusting the direct estimates from the full history data for the selection has introduced by HIV/AIDS.
- ItemOpen AccessEnvironmental health hazards on under-five mortality in sub-Saharan Africa : analysis using multilevel discrete-time hazard model(2014) Engdaw, Alehegn Worku; Adjiwanou, VisséhoEnvironmental health hazards are pathogens and chemicals in the environment, which can cause health problems. The importance of such environmental factors in child health and survival are acknowledged in the literature. However, empirical researches on the effect of environmental health hazards on child health and survival are rare in sub- Saharan Africa. This study assesses the effect of household environmental health hazards on under-five mortality in sub-Saharan Africa. The study has used DHS data sets of the following 12 countries in the region: Burkina Faso, Burundi, Cameroon, Cote d’Ivoire, Ethiopia, Gabon, Guinea, Malawi, Niger, Rwanda, Senegal and Zimbabwe. These countries constitute roughly 26 per cent of the region’s population. The study has employed principal component method to construct an index of the level of household environmental health hazards using the following indicators: water source, type of toilet facility, flooring material, type of wall, type of roof, type of cooking fuel and location of water source. I have used a multilevel discrete-time hazard model to assess the relationship between the environmental index and under-five mortality after controlling for the effects of a number of socioeconomic, biodemographic and community-level characteristics.
- ItemOpen AccessEstimating adult mortality in South Africa using information on the year-of-death of parents from the 2016 Community SurveyMambwe, Chibwe; Dorrington, RobIn developing countries, systems that collect vital statistics are usually inadequate to facilitate the direct estimation of adult mortality. This has necessitated the development of indirect methods such as the orphanhood method. These methods are however limited, i.e., the single-survey approach produces out of date estimates of mortality and the two-survey approach is affected by the differential reporting of orphanhood between two surveys. To avoid these limitations, this research considers an extension of the orphanhood approach pioneered by Chackiel and Orellana (1985) to estimate adult mortality using year-of-death data rather than the conventional form of the orphanhood data. This is because the year-of- death data can be used to produce accurate time locations to which estimates of mortality apply but more important, one can create a synthetic survey from a single survey and hence obtain more recent and accurate estimates of mortality. The single-survey orphanhood method is applied to survey data to obtain estimates of adult mortality and time location. A variation of the two-survey orphanhood method (Timæus 1991b) is also applied to survey data and the synthetic survey that is created from year-of-death data in order to derive estimates of adult mortality. In addition, the age range of respondents is extended down to age O to include year-of-death data from younger respondents on the assumption that underestimating orphanhood due to the adoption effect is minimal. This is done to investigate if the estimates derived from the two-survey method can be improved. Further, a cohort survival method that involves the calculation of a survival ratio for each age group at the first survey and the equivalent older ages groups at the second survey is applied to investigate the possibility of producing useful estimates of adult mortality based on cohort survival. The level and trend in mortality estimates calculated from the single-survey, two - survey and the cohort survival approaches are discussed and compared to the estimates from the Rapid Mortality Surveillance (RMS) which are used as a benchmark for the trend and level of adult mortality in South Africa. The estimates produced using the single-survey method appear too low, while those from the two-survey method appear to be reasonable for the conventional from of the orphanhood data. Extending the two-survey method to include younger respondents produces estimates that are too low indicating that both the conventional form of the orphanhood data and the year-of-death data suffer from the adoption effect. The cohort survival approach produces reasonable estimates that are consistent with the RMS benchmark for both the conventional form of the orphanhood data and year-of-death data.
- ItemOpen AccessEstimating adult mortality in South Africa using orphanhood and year of death data from the 2008 National Income Dynamics Study(2010) Kupamupindi, Takura; Dorrington, RobThe overall objective of this research is to investigate whether using year of death data to produce estimates of time location is a better approach than the method developed by Brass and Bamgboye (1981) and whether estimates of mortality produced using year of death data are any better than those derived using the conventional orphanhood method.
- ItemOpen AccessEstimating the level and trends of child mortality in South Africa, 1996-2006(2009) Darikwa, Timotheus Brian; Dorrington, RobThe lack of reliable data for child mortality estimation since 1998 has meant that child mortality rates for South Africa have not been updated for almost ten years now. It is the overall aim of this research to explore the possibility of determining up-to-date estimates of South Africa's infant mortality and under-five mortality rates from the 2007 Community Survey data and to use these results to describe the trend in child mortality rates since 1996.