Browsing by Author "Iloni, Karen"

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    Biplot graphical display techniques
    (1991) Iloni, Karen; Underhill, Leslie G
    The thesis deals with graphical display techniques based on the singular value decomposition. These techniques, known as biplots, are used to find low dimensional representations of multidimensional data matrices. The aim of the thesis is to provide a review of biplots for a practical statistician who is not familiar with the area. It therefore focuses on the underlying theory, assuming a standard statisticians' knowledge of matrix algebra, and on the interpretation of the various plots. The topic falls in the realm of descriptive statistics. As such, the methods are chiefly exploratory. They are a means of summarising the data. The data matrix is represented in a reduced number of dimensions, usually two, for simplicity of display. The aim is to summarise the information in the matrix and to present a visual representation of this information. The aim in using graphical display techniques is that the "gain in interpretability far exceeds the loss in information" (Greenacre, 1984). A graphical description is often more easy to understand than a numerical one. Histograms and pie charts are familiar forms of data representation to many people with no other, or very rudimentary, statistical understanding. These are applicable to univariate data. For multivariate data sets, univariate methods do not reveal interesting relationships in the data set as a whole. In addition, a biplot can be presented in a manner which can be readily understood by non-statistically minded individuals. Greenacre (1984) comments that only in recent years has the value of statistical graphics been recognised. Young (1989) notes that recently there has been a shift in emphasis, among statisticians towards exploratory data analysis methods. This school of thought was given momentum by the publication of the book "Exploratory Data Analysis" (Tukey, 1977). The trend has been facilitated by advances in computer technology which have increased both the power and the accessibility of computers. Biplot techniques include the popular correspondence analysis. The original proponents of correspondence analysis (among them Benzecri) reject probabilistic modelling. At the other extreme, some view graphical display techniques as a mere preliminary to the more traditional statistical approaches. Under the latter view, graphical display techniques are used to suggest models and hypotheses. The emphasis in exploratory data techniques such as graphical displays is on 'getting a feel' for the data rather than on building models and testing hypotheses. These methods do not replace model building and hypothesis testing, but supplement them. The essence of the philosophy is that models are suggested by the data, rather than the frequently followed route of first fitting a model. Some work has gone into developing inferential methods, with hypothesis tests and associated p-values for biplot-type techniques (Lebart et al, 1984, Greenacre, 1984). However, this aspect is not important if the techniques are viewed merely as exploratory. Chapter Two provides the mathematical concepts necessary for understanding biplots. Chapter Three explains exactly what a biplot is, and lays the theoretical framework for the biplot techniques that follow. The goal of this chapter is to provide a framework in which biplot techniques can be classified and described. Correlation biplots are described in Chapter Four. Chapter Five discusses the principal component biplot, and the link between these and principal component analysis is drawn. In Chapter Six, correspondence analysis is presented. In Chapter Seven practical issues such as choice of centre are discussed. Practical examples are presented in Chapter Eight. The aim is that these examples illustrate techniques commonly applicable in practice. Evaluation and choice of biplot is discussed in Chapter Nine.
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    The utility of computed tomography for recent-onset partial seizures in childhood
    (2006) Swingler, George H; Westwood,Anthony T R; Iloni, Karen
    Objectives. The objective was to evaluate the role of a paediatric surgical consultant at a primary health care facility. Design. Descriptive and prospective. Setting. In the process of planning and implementation of the 2010 health plan of the Provincial Government of the Western Cape, a shift occurred in the delivery of health care to children from a provincially based hospital system to a municipally based primary health care system. To contribute towards enabling this process, the Department of Paediatric Surgery at Red Cross War Memorial Children’s Hospital established a paediatric surgical day clinic at a local community health centre during 2001. Subjects. Information was obtained from patient data sheets containing details of consultations at the sub-specialist surgical clinic at Michael Mapongwana Community Health Centre. Results. Over a 58-month period 1 171 children were seen, of whom 655 were male and 427 female. Their ages ranged from 0 to 19 years, the largest group being under 1 year. Eighty per cent of patients were accompanied by their mothers. The correct diagnosis was established by the nurse practitioners in 71%. General paediatric surgical conditions predominated, followed by medical, dermatological, orthopaedic, trauma, otolaryngo-pharyngology, infectious diseases, ophthalmology, urology, neurosurgery, malignancy and maxillofacial conditions. The details are set out in the report. In total 597 patients were referred directly to an appropriate care facility and 574 patients could be managed entirely at the clinic level. Conclusions. This study demonstrated the significant public health problem of paediatric surgical disease. It emphasised the preventative and cost-effective role of a surgical clinic at primary health care level. The clinic allowed for timely surgical intervention in 65% of surgical cases, thereby decreasing inappropriate tertiary referrals. We believe that bringing specialists into the community can only strengthen the 2010 health care plan.
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    The utility of computed tomography for recent-onset partial seizures in childhood
    (2006) Swingler, George H; Westwood, Anthony T R; Iloni, Karen
    Objectives. To determine the diagnostic yield of computed tomography (CT) of the head in children presenting for the first time with partial seizures in a region with a high prevalence of tuberculosis and neurocysticercosis. Design. Prospective cohort study Setting. The secondary-level ambulatory service of Red Cross Children’s Hospital, Cape Town. Subjects. Children aged 6 months - 12 years with a first partial seizure. Outcome measures. Abnormal CT findings; clinically unsuspected abnormal CT findings. Results. Of 118 enrolled children, CT findings were available for 94 (80%). Sixteen (33%) of 49 children scheduled to return later for an initial CT scan failed to do so. Thirty-two scans (34%) were reported normal, 45 (48%) showed single or multiple granulomas, and 17 (18%) showed other findings. All 8 children with persistent specific CT findings were suspected of having the condition before CT scan. Of 68 cases with prospectively recorded clinically expected CT findings, normal scans were expected in 2 cases (3%) and occurred in 33 cases (49%). Conclusions. Routine CT scan for children presenting with a first partial seizure in an area with a high prevalence of neurocysticercosis failed to identify findings other than neurocysticercosis that meaningfully altered clinical management. Assuming a 70% relative reduction of seizures with albendazole treatment for neurocysticercosis, routine CT scanning in the study population would require 11 scans and 5 courses of albendazole to prevent 1 child from having seizures, compared with no CT scans and 11 courses of albendazole with blanket use of albendazole.