D. Litt et Phil.

In this paper we first show that the gains achievable by integrating pricing and inventory control are usually small for classical demand functions. We then introduce reference price models and demonstrate that for this class of demand functions the benefits of integration with inventory control are substantially increased due to the price dynamics. We also provide some analytical results for this more complex model. We thus conclude that integrated pricing/inventory models could repeat the success of revenue management in practice if reference price effects are included in the demand model and the properties of this new model are better understood. (authors' abstract)

More than a decade of research has indicated that individuals who have experienced traumatic events may report positive psychological changes as a result of their struggle to cope with the impact of the event. This cluster of changes has been labelled posttraumatic growth (PTG). Several measurement instruments have been developed to quantify such growth, one of the most widely used being the Posttraumatic Growth Inventory (PTGI) developed by Tedeschi and Calhoun (1996). The objective of the present study was to conduct a confirmatory factor analysis (CFA) of the PTGI on data yielded by a South African sample, to determine if the hypothesised factor structure showed appropriate fit in this context. Analyses were performed with three hypothesised models: the five factor model, the three factor model and the model of posttraumatic growth as a unitary factor. Whilst the results of the CFA did not provide overt support for the adequate fit of the models tested, it did yield a profile of PTG in the South African sample that is similar to that of samples from other countries of origin. The findings implied that the factorial validity of the PTGI is unclear and the inventory may require modification for use in the South African context. This highlighted the need for further investigation in order to provide a comprehensive exploration of the PTGI and its applicability in this context. This is in line with the current focus on the socio-cultural and contextual elements that may influence the perception of PTG.

The Five-Factor Model (FFM) of personality is one of the prominent models in contemporary psychology and defines personality in terms of five broad factors, namely, Neuroticism, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness. Recent research, however, questions the applicability of the FFM in non-Western cultures, suggesting that it is not exhaustive enough and that it does not account for some other personality factors, most notably Individualism/Collectivism. Therefore, this study investigated whether the FFM of personality is related to Individualism/Collectivism in a sample of South African students. A total of 176 questionnaires were completed by students from the University of the Witwatersrand. The questionnaire contained the individualism/collectivism (INDCOL) scales and the Basic Traits Inventory (BTI) which is a South African instrument based on the FFM. Results indicate that there were no significant relationships between the five factors and Individualism/Collectivism. In addition no significant difference was found between race and the five factors and Individualism/Collectivism. There were also no significant differences between home language and the five factors and Individualism/Collectivism.

While the validity of posttraumatic growth has been repeatedly questioned, the prevalence of growth after exposure to trauma is widely established. Perceptions of posttraumatic growth were examined in a sample of South African adults (N = 135). Participants completed a selfadministered battery of questionnaires via an online trauma survey or in paper format. Data specific to the nature of the traumatic event, particularly the type of trauma, time since the traumatic event, the impact of the event and perceived threat of the event, were collected along with posttraumatic growth (PTG) scores. Age, gender and perceived social support were also assessed as variables. Results of the multivariate analyses indicated that PTG differed significantly as a function of the type of traumatic event. PTG also differed according to the time since the traumatic event, although the relationship was complex and subject to the additional moderating factors of depression, anxiety and stress. Examination of the growth factors further revealed a differential pattern of PTG according to event type, and a variable pattern of relationship to social support, perceived threat and impact of the trauma. The findings supported the view of PTG as a complex, highly subjective perception of growth that may involve many levels and aspects of change. The nature of PTG is important in the context of South Africa, for the individuals, and their families, who have been exposed to high levels of crime, violence, chronic illness and road accidents, and for a nation in the process of rebuilding itself.

Personality psychology became an identifiable discipline in the social sciences in the 1930s when Allport (1937) published an article on the psychological interpretation of personality. The field of personality traditionally emphasised the study of the whole person, the dynamics of human motivation and the identification and measurement of individual differences (McAdams, 1997). Since the publication of Allport’s article, personality has been extensively researched and several theories exist that attempt to organise and explain the differences in human behaviour. Personality instruments are based on personality theories and aim to assist psychologists with the prediction of human behaviour. Psychologists use personality instruments as part of a selection battery to assist organisations with the screening and selection of individuals who have the potential to be successful within a specific work environment. The Basic Traits Inventory (BTI), a personality instrument that is based on the Five-Factor model, was developed in South Africa by Taylor and De Bruin (2006). The BTI is a valid and reliable personality instrument as indicated by results from research by Taylor (2004), Taylor and De Bruin (2006) and Taylor (2008) on its utility within the multicultural and multilingual environment of South Africa. Taylor (2008) nevertheless identified some problematic items when she analysed the construct, item, and response bias of the BTI across cultures for three language groups – Afrikaans, English and indigenous African languages – and consequently indicated the need for further research in this regard. The current study therefore explores the possible bias of the items of the BTI, and uses a sample large enough to analyse each of the eleven of the official languages of South Africa separately. The study focuses on the impact of the eleven official languages of South Africa on assessment of the Big Five personality factors with the BTI. The actual sample consisted of 105 342 respondents, resulting in the sub-samples per official language group being larger than 1 000. Each of the eleven official South African language groups could therefore be analysed separately, which has not been possible in previous studies. Analysis of the responses of the total sample to the BTI items generally yielded high reliability in terms of Cronbach alpha coefficients (α) and the Person Separation Index (PSI). The results were reported as follows: Extraversion (α=.86; PSI=.85); Neuroticism (α=.89; PSI=.86); Conscientiousness (α=.93; PSI=.88); Openness to experience (α=.90; PSI=.84); Agreeableness (α=.94; PSI=.86); and Social desirability (α=.72; PSI=.70). MANOVA results indicated statistically significant differences between the mean values of each of the BTI factors for the different language groups. Rasch analysis methods were used to further analyse the differences in terms of item responses for each of the eleven official language groups in South Africa. Respondents generally interpret and endorse the items of a personality instrument according to their intrinsic personality characteristics and their interpretation of the words used in the items of the personality instrument. In order to assess the respondents’ understanding of the administration language, English, two English proficiency tests were administered together with the BTI. The combined English proficiency scores were used to differentiate between respondents who understood English very well (top 25% – high English proficiency group) and those who struggled to understand English terminology (bottom 25% – low English proficiency group). Rasch analysis techniques were used to analyse the data for the whole sample as well as for the high and low English proficiency groups. Some items showed statistically significant differences for the language groups, indicating item bias in the BTI. Contrary to expectation, a larger number of biased items were indicated for the higher English proficiency group than for the total group or for the low English proficiency group. Due to the number of biased items for the high English proficiency group, it was concluded that the differences between the eleven official language groups may be a result of the differences in the intrinsic personality characteristics of the respondents, rather than measurement errors or item bias of the BTI instrument. Further research in this regard was recommended. The current study confirms that home language and English proficiency, as indicators of the level of understanding of the language in which the personality instrument was administered, undeniably influence the individual’s response pattern. Far fewer items indicated bias than those identified in Taylor’s (2008) study, where a smaller sample was used and language groups were combined. Despite some BTI items showing bias, the conclusion was reached that this personality instrument can be used with confidence to assess personality traits in persons speaking any of the eleven official South African languages. / Industrial and Organisational Psychology / D. Comm. (Industrial and Organisational Psychology)

The world is getting connected in both small and bigger systems. Internet of Things (IoT) has flourished the past years and we no longer just connect our computers and phones but also our cars, wallets, keys and even the furniture and lighting in homes are talking. It is time to take things one step further, give your food and supplies a voice. This master thesis has the purpose to construct a smart inventory using the IoT. Its outcome is a prototype that consists of three main parts: 1) a number of sensor nodes to measure what products are left, 2) a hub to collect the inventory from the sensor nodes through acoustic communication and store it, and 3) an app on a mobile device to receive the inventory from a hub via Bluetooth and display it in a list for the user. The acoustic communication between the sensor node and the hub are thoroughly investigated taking into account the distance and angle as well as reliability. The Bluetooth communication between the hub and the mobile device with the app can be established automatically when the app is opened or when the user requests an update. The finished prototype has been tested and its performance evaluated. The results show that it functions with great satisfaction, being capable of measuring inventory, storing it and display it on the app. The sensor node and hub have highly reliable communicate within the distance of 1.9 m, a horizontal angle of 25 degrees and a vertical angle of 30 degrees. When the system is exposed to a lot of disturbance it has a reliability of 66% and the Bluetooth connection between the hub and the app can automatically connect about 70% of the times. This smart inventory system can be used in homes, storage rooms, offices, workshops and stores without Internet connection so that no one outside of Bluetooth coverage can get the information, or be expand with Internet connection so that the inventory can be updated anywhere and anytime around the world.

Em diversos setores, em especial no automotivo, uma boa gestão dos estoques de peças de reposição tem impacto significativo na satisfação dos clientes e em sua fidelidade aos fabricantes. Neste trabalho foram estudadas diferentes políticas de gestão dos estoques de peças de reposição, para comparar seu desempenho e elaborar recomendações para seu uso. Foram comparados 17 conjuntos de políticas que envolvem diferentes abordagens no registro das demandas (dados individuais de cada pedido versus dados agregados em janelas de tempo semanais e mensais), modelos de previsão (média móvel, Croston modificado SBA) e diferentes formas de modelar a distribuição da demanda durante o Lead-time de ressuprimento (Normal, Gama, Binomial Negativa, composta Poisson-Normal, composta Poisson-Gama). Cada um desses 17 conjuntos de políticas foi simulado sob duas dinâmicas de reparametrização (mensal e semestral) e para quatro objetivos diferentes do nível de serviço (TFR: Target Fill Rate), totalizando 136 simulações para cada item do estoque (SKU). Foram considerados 10.032 SKU\'s de uma montadora de automóveis instalada no Brasil, com um histórico de seis anos de movimentação. Diferentes recomendações foram elaboradas conforme categorização dos itens já existente na literatura. Os resultados apontaram recomendações distintas para cada TFR, incluindo combinações de todas as alternativas estudadas, descartando apenas o uso das distribuições Normal, composta Poisson-Normal e composta Poisson-Gama. Sugere-se que as recomendações sirvam como guia para o uso desses modelos pelos praticantes. / In many areas, including automotive, a good spare parts inventory management can substantially affect customer satisfaction and their loyalty to the brands. Different spare parts inventory control policies were evaluated in this study, aiming to compare their performance and write recommendations for their usage. Seventeen policy sets were compared, including different approaches in recording demand data (individual orders data against time bucket records weekly and monthly), different demand forecasting methods (simple moving average, Syntetos-Boylan-approximation SBA) and different models for demand distribution during lead-time (Normal, Gama, Negative Binomial, compound Poisson-Normal, compound Poisson-Gama). Each policy set was simulated under two revision frequencies (monthly and semi-annually) and four different Target-Fill-Rates (TFR), totalizing 136 simulation runs for each SKU. Database included movement of 10.032 SKU´s during last 6 years from an automaker installed in Brazil. Results pointed different recommendations for existing classification schemes and under each TFR. Recommendations included all studied alternatives, discarding only the usage of Normal, compound Poisson-Normal and compound Poisson-Gama for demand distribution during lead-time. Practitioners are stimulated to use these recommendations as a guideline.

O objetivo deste trabalho é comparar o desempenho de modelos de estoque em uma grande diversidade de situações de demanda e custos. Os modelos de estoque comparados são os tradicionais Reposição do Máximo, Reposição da Base e Lote Fixo, com políticas de revisões periódicas e contínuas, e um modelo derivado da lógica dos sistemas Material Requirements Planning (MRP), aqui denominado Cálculo de Necessidades, que utiliza previsões de demanda para o dimensionamento dos pedidos de reposição de estoque. As séries temporais de demanda, por seu lado, são geradas a partir de tendências e sazonalidades definidas, sobre as quais se acrescenta o componente irregular aleatório. Numa primeira etapa, simulação e busca em vizinhança são utilizadas na seleção do melhor modelo de previsão de demanda, a cada série temporal, para gerar as previsões do modelo Cálculo de Necessidades. Suavização Exponencial Simples, o Método Linear de Holt, Suavização Exponencial Simples com Sazonalidade e o Método de Tendência e Sazonalidade de Holt-Winters são os modelos de previsão utilizados nesta seleção. Numa segunda etapa, simulação e busca em vizinhança são também utilizadas para a otimização dos parâmetros dos sete modelos de estoque para cada série temporal. A soma dos custos médios de Pedido, de Armazenagem e de Falta é utilizada como variável de medição do desempenho dos modelos. Os resultados mostram um desempenho superior do modelo de Cálculo de Necessidades, em quase todos os ambientes testados, secundado pelo modelo contínuo de Reposição do Máximo. Mostram, ainda, um desempenho fraco do modelo contínuo de Reposição da Base, fundamento do conhecido modelo kanban, o que contraria sua forte recomendação como modelo robusto. Este trabalho tem como principal contribuição a evidência da superioridade do modelo de Cálculo de Necessidades sobre os modelos tradicionais nas condições da pesquisa efetuada. / The objective of this study is to compare the performance of inventory models in a large range of costs and demand environments. The compared models are the traditional periodic and continuous Up to Maximum Inventory Level, Base Stock and Fixed Lot Size, and another model, based on the Material Requirements Planning (MRP) logic and here referred to as Requirements Planning, which uses demand forecast to quantify the acquisition decisions. In the first step, simulation and neighborhood search are used to select the best of 4 forecasting models, which generates the forecasts to the Requirements Planning model. Single Exponential Smoothing, Holt\'s linear method, Single Exponential Smoothing with seasonality, and Holt-Winters\' trend & seasonality method are these 4 models. In the second step, simulation and neighborhood search are used again to optimize the inventory models parameters. The items\' demand time series are based on trends and seasonality defined arbitrarily plus the addition of a irregular random component. The period average Purchase, holding, shortage and total costs are calculated and the models are ranked, based on the total cost criterion. The results show the superior performance of the Requirements Planning model in practically all tested conditions, with the continuous Up to Maximum Inventory Level in a secondary position. The results show, too, the poor performance of the continuous Base Stock model, base of the Kanban system, in opposition to its actual hard recommendation as robust model. This study has, as major contribution, the evidence of the Requirements Planning model superior performance compared with the traditional inventory models.

Este trabalho propõe um método de análise do trade-off entre o buffer de capacidade de produção e o buffer de estoque, necessários para garantir o bom desempenho de um sistema sujeito a variações de demanda. A análise envolve a definição de um sistema de produção e a construção de um modelo de simulação. A simulação é realizada num sistema formado por uma única estação de trabalho, com mix de 10 produtos, controlados por um sistema kanban, que é considerado por muitos autores inadequado para operar em ambientes cuja demanda não é estável. Os resultados mostram que o buffer de capacidade proporciona vantagens operacionais e de custo ainda que sujeito a maiores níveis de variação de demanda. / This research proposes a method to analyze the trade-off between the production capacity buffer and the inventory buffer, required to guarantee high performance levels in a system with demand variation. The analysis involves a production system delineation and the development of a simulation model. The system simulated is a single-stage production system, with mix of ten products, controlled by a kanban system, which is classified by several authors as not recommended in environments with unstable demand. The results indicate that the production capacity buffer enables operational and cost advantages, even if the production system is under higher demand variation.