scholarly journals The effect of transient exposures on the risk of an acute illness with low hazard rate

Biostatistics ◽  
2004 ◽  
Vol 5 (2) ◽  
pp. 239-248 ◽  
Author(s):  
N. G. Becker
Keyword(s):  
2012 ◽  
Vol 82 (4) ◽  
pp. 260-266 ◽  
Author(s):  
Salah E. Gariballa ◽  
Sarah J. Forster ◽  
Hilary J. Powers

Background: Although a number of studies have reported raised total plasma homocysteine (tHcy) concentrations in free-living older people, there are no data on homocysteine response to a mixed nutrient supplement in older patients. A raised plasma homocysteine concentration in older patients is partly a reflection of their co-morbidity, including impaired renal function, and there is uncertainty about the extent to which dietary interventions can improve plasma tHcy. Aim: To determine the plasma tHcy response to dietary supplements during acute illness. Methods: Two-hundred and thirty-six hospitalized, acutely ill older patients, who were part of a randomized double-blind placebo-controlled trial, were assigned to receive a daily oral nutritional supplement drink containing 1.3 mg of vitamin B2, 1.4 mg of vitamin B6, 1.5 μg of B12, 200 μg of folic acid, or a placebo, for 6 weeks. Outcome measures were plasma tHcy concentration at baseline, 6 weeks, and 6 months. Results: The mean plasma tHcy concentration fell among patients given the supplements (mean difference 4.1 µmol/L [95 % C.I, 0.14 to 8.03), p = 0.043], but tHcy concentration increased between 6 weeks and 6 months, after patients stopped taking the supplements [mean difference -2.0 µmol/L (95 % C.I, -03.9 to -0.18), p = 0.033]. About 46 % of patients in the placebo group and 55 % of patients in the supplement group had hyperhomocysteinemia (>14 µmol/L) at baseline compared with 45 % and 29 % at the end of the treatment period. Conclusions: A mixed nutrient supplement containing physiological amounts of B vitamins significantly reduced plasma tHcy concentrations in older patients recovering from acute illness.


2008 ◽  
Vol 47 (02) ◽  
pp. 167-173 ◽  
Author(s):  
A. Pfahlberg ◽  
O. Gefeller ◽  
R. Weißbach

Summary Objectives: In oncological studies, the hazard rate can be used to differentiate subgroups of the study population according to their patterns of survival risk over time. Nonparametric curve estimation has been suggested as an exploratory means of revealing such patterns. The decision about the type of smoothing parameter is critical for performance in practice. In this paper, we study data-adaptive smoothing. Methods: A decade ago, the nearest-neighbor bandwidth was introduced for censored data in survival analysis. It is specified by one parameter, namely the number of nearest neighbors. Bandwidth selection in this setting has rarely been investigated, although the heuristical advantages over the frequently-studied fixed bandwidth are quite obvious. The asymptotical relationship between the fixed and the nearest-neighbor bandwidth can be used to generate novel approaches. Results: We develop a new selection algorithm termed double-smoothing for the nearest-neighbor bandwidth in hazard rate estimation. Our approach uses a finite sample approximation of the asymptotical relationship between the fixed and nearest-neighbor bandwidth. By so doing, we identify the nearest-neighbor bandwidth as an additional smoothing step and achieve further data-adaption after fixed bandwidth smoothing. We illustrate the application of the new algorithm in a clinical study and compare the outcome to the traditional fixed bandwidth result, thus demonstrating the practical performance of the technique. Conclusion: The double-smoothing approach enlarges the methodological repertoire for selecting smoothing parameters in nonparametric hazard rate estimation. The slight increase in computational effort is rewarded with a substantial amount of estimation stability, thus demonstrating the benefit of the technique for biostatistical applications.


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