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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Algorithmica 25 (1999), S. 37-57 
    ISSN: 1432-0541
    Keywords: Key words. On-line fast multiple algorithm, Smoothing, Kernel regression, Nonparametric density estimation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. Nonparametric density estimation has broad applications in computational finance especially in cases where high frequency data are available. However, the technique is often intractable, given the run times necessary to evaluate a density. We present a new and efficient algorithm based on multipole techniques. Given the n kernels that estimate the density, current methods take O(n) time directly to sum the kernels to perform a single density query. In an on-line algorithm where points are continually added to the density, the cumulative O(n 2 ) running time for n queries makes it very costly, if not impractical, to compute the density for large n . Our new Multipole-accelerated On-line Density Estimation (MODE) algorithm is general in that it can be applied to any kernel (in arbitrary dimensions) that admits a Taylor series expansion. The running time for a density query reduces to O (logn) or even constant time, depending on the kernel chosen, and, hence, the cumulative running time is reduced to O (n logn) or O(n) , respectively. Our results show that the MODE algorithm provides dramatic advantages over the direct approach to density evaluation. For example, we show using a modest computing platform that on-line density updates and queries for 1 million points and two dimensions take 8 days to compute using the direct approach versus 40 seconds with the MODE approach.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-7284
    Keywords: Air pollution ; Asthma ; Prevalence ; Risk factors ; South Africa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The prevalence of asthma and respiratory symptoms in south-central Durban, one of the most heavily polluted areas of South Africa, has been determined using a cross-sectional survey of 213 households in the communities of Merewent (97% Indians) and Austerville (98% coloreds). The study population consisted of 367 children (less than 17 years old) and 693 adults. About 10% of the children and 12% of adults reported doctor diagnosed asthma. The self-reported prevalence rates for wheezing (37–40%) and attacks of shortness of breath with wheeze (16–28%) were much higher than that for doctor diagnosed asthma and common co-occurrence of the three symptoms is found. The prevalence rates for other respiratory symptoms include 33–35% for chronic cough, 31–32% for chronic phlegm, 44–50% for frequent blocked-runny nose, and 16–27% for sinusitis. Factors in the community that were associated with asthma, wheeze and shortness of breath with wheeze among the adult population included cigarette smoking, use of insecticides (coils and pump spray) and home ownership. An association between asthma among children and a number of household risk factors including dampness, carpet, pets or use of pesticides was not apparent in the community. Asthma prevalence was strongly correlated with missing of school by children (odds ratio (OR): 44; 95% confidence interval (CI): 13–141). The study serves to draw attention to a growing but neglected public health problem in urban areas of Africa.
    Type of Medium: Electronic Resource
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