D-optimal designs for drug synergy.

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.This thesis is focused on the construction of optimal designs for detecting drug interaction using the two-variable binary logistic model. Two specific models are considered: (1) the binary two-variable logistic model without interaction, and (2) the binary two-variable logistic model with interaction. The two explanatory variables are assumed to be doses of two drugs that may or may not interact when jointly administered to subjects. The main objective of the thesis is to algebraically construct the optimal designs. However, numerical computations are used for constructing optimal designs in cumbersome cases. The problem of constructing optimal designs is to allocate weights to specific points of the design space in such a way that information associated with model parameters is maximized and the variances of the mean responses are minimized. Specifically, the D-optimality criterion discussed in this thesis minimizes the determinant of the asymptotic variance-covariance matrix of the estimates of the model parameters. The number of support points of the D-optimal designs for the two- variable binary logistic model without interaction varies from 3 to 6. Support points are equally weighted only in case of the 3-point designs and in some special cases of the 4-point designs. The number of support points of the D-optimal designs for the two-variable binary logistic model with interaction varies from 4 to 8. Support points are equally weighted only in case of the 4-point designs and in some special cases of 8-point designs. Numerous examples are given to illustrate theoretical results

Patients’ perspectives of acceptability of ART, TB and maternal health services in a subdistrict of Johannesburg, South Africa

Abstract: Background: The field of acceptability of health services is emerging and growing in coherence. But there are gaps, including relatively little integration of elements of acceptability. This study attempted to analyse collectively three elements of acceptability namely: patient-provider, patient-service organisation and patient-community interactions. Methods: Mixed methods were used to analyse secondary data collected as part of the Researching Equity in Access to Health Care (REACH) study of access to tuberculosis (TB) treatment, antiretroviral therapy (ART) and maternal health (MH) services in South Africa’s public health sector. Results: Provider acceptability was consistently high across all the three tracer services at 97.6% (ART), 96.6% (TB) and 96.4% (MH). Service acceptability was high only for TB tracer (70.1%). Community acceptability was high for both TB (83.6%) and MH (96.8%) tracers. Conclusion: Through mixed methods, this paper provides a nuanced view of acceptability of health services

Cryptocurrencies and Tokens Lifetime Analysis from 2009 to 2021

The success of Bitcoin has spurred emergence of countless alternative coins with some of them shutting down only few weeks after their inception, thus disappearing with millions of dollars collected from enthusiast investors through initial coin offering (ICO) process. This has led investors from the general population to the institutional ones, to become skeptical in venturing in the cryptocurrency market, adding to its highly volatile characteristic. It is then of vital interest to investigate the life span of available coins and tokens, and to evaluate their level of survivability. This will make investors more knowledgeable and hence build their confidence in hazarding in the cryptocurrency market. Survival analysis approach is well suited to provide the needed information. In this study, we discuss the survival outcomes of coins and tokens from the first release of a cryptocurrency in 2009. Non-parametric methods of time-to-event analysis namely Aalen Additive Hazards Model (AAHM) trough counting and martingale processes, Cox Proportional Hazard Model (CPHM) are based on six covariates of interest. Proportional hazards assumption (PHA) is checked by assessing the Kaplan-Meier estimates of survival functions at the levels of each covariate. The results in different regression models display significant and non-significant covariates, relative risks and standard errors. Among the results, it was found that cryptocurrencies under standalone blockchain were at a relatively higher risk of collapsing. It was also found that the 2013–2017 cryptocurrencies release was at a high risk as compared to 2009–2013 release and that cryptocurrencies for which headquarters are known had the relatively better survival outcomes. This provides clear indicators to watch out for while selecting the coins or tokens in which to invest

Demographic and angioarchitectural features associated with seizures presentation in patients with brain arteriovenous malformations in Durban, KwaZulu-Natal, South Africa

Background: Brain arteriovenous malformations (AVMs) often present with epileptic seizures which carry standard mortality rate two to three folds higher than in the general population, yet preventative eradication of these lesions remains controversial. The aim of this study was to determine the demographic and angioarchitectural features associated with clinical presentation of seizures in patients with brain AVMs. Methods: We conducted a retrospective chart review of all consecutive patients who presented to three interventional neuroradiology hospitals, with brain AVMs in Kwazulu-Natal, South Africa, over a period of 10years. The demographic and clinical presentations were derived from patient's electronic medical records. Radiological features were determined using axial Computerized Topography (CT) or Magnetic Resonance Imaging (MRI) Scan. Angioarchitectural features were determined from Digital Subtraction Angiography (DSA). Simple and multiple logistic regression models were used to identify factors associated with the risk of seizure as initial presentation in brain AVMs. Results: The analysis identified race/ethnicity, nidus size and location as the predictors of seizure presentation. By multiple logistic regression analysis, African-black race (OR=4.7; 95%CI: 1.15–19.60), brain AVM nidus >3cm in diameter, (OR=4.4; 95%CI: 1.7−11.42) and cortical lobar location (OR=13.6; 95%CI: 2.80−65.14) were found to be significant predictors of brain AVM-associated seizures. Conclusion: Improved knowledge of specific morphological factors associated with brain AVM epilepsy could aid in the formulation of appropriate therapeutic strategies for control and/or cure of these brain AVM-associated seizures. Keywords: Angioarchitecture, Arteriovenous malformations, Brain, Demographics, Seizure