Exact Inference for the Linear Model with Groupwise Heteroscedasticity

Exact inference on a single coefficient in a linear regression model, as introduced by Bekker (1997), is elaborated for the case of normally distributed heteroscedastic disturbances. Instead of approximate inference based on feasible generalized least squares, exact confidence sets are formulated based on partial rotational invariance of the distribution of the vector of disturbances. The approach is applied to the random-effects and fixed-effects models for panel data.

Development Studies Working Paper, no. 5

A rural development project is currently under way in the Amatola Basin, Ciskei. This paper introduces the project and outlines the socio-economic and agricultural conditions current in the area. An overview of present project activities is included. It then attempts to identify a number of potential and actual human and structural constraints operating on the implementation of the project. Such constraints arise out of the existing agricultural system in the project area, as well as out of the state bureaucratic structures operating in Ciskei, and the agency implementing the project itself. One aim is to identify the units involved in dryland cultivation. This is done by tracing ties of cooperation between cultivating households in one Amatola village. It will be shown, in this village at least, that the household does not form the main unit of cultivation. A second aim of this paper is to show that checks on rural development in general should not be sought solely within the area under consideration, but derive to an important degree from outside sources.Digitised by Rhodes University Library on behalf of the Institute of Social and Economic Research (ISER

Effect of quantum nuclear motion on hydrogen bonding

This work considers how the properties of hydrogen bonded complexes, D-H....A, are modified by the quantum motion of the shared proton. Using a simple two-diabatic state model Hamiltonian, the analysis of the symmetric case, where the donor (D) and acceptor (A) have the same proton affinity, is carried out. For quantitative comparisons, a parametrization specific to the O-H....O complexes is used. The vibrational energy levels of the one-dimensional ground state adiabatic potential of the model are used to make quantitative comparisons with a vast body of condensed phase data, spanning a donor-acceptor separation (R) range of about 2.4-3.0 A, i.e., from strong to weak bonds. The position of the proton and its longitudinal vibrational frequency, along with the isotope effects in both are discussed. An analysis of the secondary geometric isotope effects, using a simple extension of the two-state model, yields an improved agreement of the predicted variation with R of frequency isotope effects. The role of the bending modes in also considered: their quantum effects compete with those of the stretching mode for certain ranges of H-bond strengths. In spite of the economy in the parametrization of the model used, it offers key insights into the defining features of H-bonds, and semi-quantitatively captures several experimental trends.Comment: 12 pages, 8 figures. Notation clarified. Revised figure including the effect of bending vibrations on secondary geometric isotope effect. Final version, accepted for publication in Journal of Chemical Physic

Logistics-related customer complaints in the South African retail industry

Abstract: Intense competition in the South African fast-moving customer goods (FMCG) retailing industry often results in price wars that encourage customer switching behaviour. Time and place utility provided by distribution, equates to customer service and forms part of the competitive strategy of retailers. Solving last-mile logistical problems in-store could be a valuable strategy in differentiation and building customer loyalty. The purpose of this study was to explore the nature of logistics-related customer complaints concerning South African mass grocery retailers (MGR) as lodged on customer complaints website Hellopeter.com, pertaining to the three largest MGR groups for the period of one year ending August 2016..

Evaluating the implementation of injury prevention strategies in rugby union and league: a systematic review using the RE-AIM framework

Rugby (union and league) has come under intense scrutiny due to its injury risk. Various interventions have been introduced to protect players from injury, with many deemed efficacious and advocated for use across various worldwide contexts. However, their implementation is less clear. The objective of this systematic review was to determine whether injury prevention interventions in rugby have evaluated their ‘reach’, ‘effectiveness’, ‘adoption’, ‘implementation’ and ‘maintenance’ as per the RE-AIM Multi-Dimension Item Checklist. Six electronic databases were searched in November 2019. Inclusion criteria included: English language, peer-reviewed journal article, original research, field-based rugby code, prospective intervention. Of the 4253 studies identified, 74 met the full inclusion criteria. Protective equipment, predominately mouthguards, was the intervention of interest in 44 studies. Other interventions included multimodal national injury prevention programmes, law changes and neuromuscular training programmes. ‘Effectiveness’ was the highest scoring RE-AIM dimension (55%), followed by ‘reach’ (26%). All other RE-AIM dimensions scored below 20%. Research currently focuses on determining intervention ‘effectiveness’. For injury prevention strategies to have their desired impact, there must be a shift to address all determinants associated with implementation. Consideration should be given to how this can be achieved by adopting specific reporting checklists, research frameworks and study designs

Childhood tuberculosis infection and disease: A spatial and temporal transmission analysis in a South African township

Background. Tuberculosis (TB) remains a leading cause of mortality and morbidity in South Africa. While adult TB results from both recent and past infection, childhood TB results from recent infection and reflects ongoing transmission despite current TB control strategies.Setting. A South African community with high rates of TB and HIV disease.Outcomes. A Geographic Information System was used to spatially and temporally define the relationships between TB exposure, infection and disease in childre

The Hannan Crusaid Treatment Centre – early beginnings and lessons learnt

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