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  • 1990-1994  (2)
  • Asymptotic approximations  (1)
  • Crohn's disease  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Statistics and computing 2 (1992), S. 161-171 
    ISSN: 1573-1375
    Keywords: Asymptotic approximations ; bootstrap calibration ; coverage accuracy ; resampling ; saddlepoint methods ; tail probability approximations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Standard algorithms for the construction of iterated bootstrap confidence intervals are computationally very demanding, requiring nested levels of bootstrap resampling. We propose an alternative approach to constructing double bootstrap confidence intervals that involves replacing the inner level of resampling by an analytical approximation. This approximation is based on saddlepoint methods and a tail probability approximation of DiCiccio and Martin (1991). Our technique significantly reduces the computational expense of iterated bootstrap calculations. A formal algorithm for the construction of our approximate iterated bootstrap confidence intervals is presented, and some crucial practical issues arising in its implementation are discussed. Our procedure is illustrated in the case of constructing confidence intervals for ratios of means using both real and simulated data. We repeat an experiment of Schenker (1985) involving the construction of bootstrap confidence intervals for a variance and demonstrate that our technique makes feasible the construction of accurate bootstrap confidence intervals in that context. Finally, we investigate the use of our technique in a more complex setting, that of constructing confidence intervals for a correlation coefficient.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Digestive diseases and sciences 37 (1992), S. 705-708 
    ISSN: 1573-2568
    Keywords: polyethylene glycol 400 ; intestinal permeability ; small bowel permeability ; Crohn's disease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract An altered small bowel permeability may be implicated in the pathogenesis of Crohn's disease. Intestinal permeability, using polyethylene glycol 400 (PEG 400) as the orally ingested probe, was assessed in 45 patients with Crohn's disease (ilealN=14, ileocolonicN=9, colonicN=10, postresectionN=12), 20 first-degree relatives, and 31 controls. PEG 400 excretion was measured using a direct injection HPLC method, and results are expressed as percent of dose recovered in urine (median and range). No quantitative differences in the recovery of PEG-400 were found [Crohn's patients 21.9% (6.1–39.9), relatives 23.7% (4.9–39.9), controls 25.0% (4.5–39.7)]. In all groups, the composition of ingested and recovered PEG-400 was similar and no selective permeability to any molecular weight species was found. Disease site did not influence probe recovery [ileal 23.8% (7.7–30.6), ileocolonic 22.6% (14.4–33.8), colonic 27.8% (9.5–33.5)]. Resected patients had significantly lower PEG-400 recovery [18.8% (8.1–39.9)] than nonresected patients [23.5% (6.1–33.8%)P〈0.02]. The data suggest either that altered intestinal permeability is not a factor in Crohn's disease or that PEG-400 is not a suitable probe.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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