2,638 research outputs found
Kernel Estimation of Rate Function for Recurrent Event Data
No full textRecurrent event data are largely characterized by the rate function but smoothing techniques for estimating the rate function have never been rigorously developed or studied in statistical literature. This paper considers the moment and least squares methods for estimating the rate function from recurrent event data. With an independent censoring assumption on the recurrent event process, we study statistical properties of the proposed estimators and propose bootstrap procedures for the bandwidth selection and for the approximation of confidence intervals in the estimation of the occurrence rate function. It is identified that the moment method without resmoothing via a smaller bandwidth will produce a curve with nicks occurring at the censoring times, whereas there is no such problem with the least squares method. Furthermore, the asymptotic variance of the least squares estimator is shown to be smaller under regularity conditions. However, in the implementation of the bootstrap procedures, the moment method is computationally more efficient than the least squares method because the former approach uses condensed bootstrap data. The performance of the proposed procedures is studied through Monte Carlo simulations and an epidemiological example on intravenous drug users. Copyright 2005 Board of the Foundation of the Scandinavian Journal of Statistics..
Entrance assessment of exotic highly pathogenic avian influenza through air-passenger violation risk model.
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Gibberellin-induced flowering in sexually defective Remusatia vivipara (Araceae)
No full textRemusatia vivipara is an epiphyte of possibly ornamentally and medically important plant, but flowering is rare in fields. The present experiments were conducted to study the influences of different concentrations of gibberellic acid (GA3) and tuber sizes on the flower initiation, inflorescence characteristics and vegetative growth in R. vivipara. GA3 concentration as low as 25 mg L-1 could induce flowering. The results of a binary logistic regression analysis indicated that the flowering was significantly associated both with GA3 concentration and tuber size. However, comparing with the non-GA3 treated tubers, different GA3 concentrations did not significantly affect flowering. The result also showed no significant effect induced by GA3 treatments on the number of days to flower. In contrast, the Wald statistic revealed that both tuber size (2.51–3.00 cm) and tuber size (3.01–3.50 cm) made more significant contributions to the prediction of flowering. Tuber diameters above 3.01 cm with 100 mg L-1 GA3 treatment could bring all plants to flower. Results of canonical discriminant analysis and ANOVA tests indicated that there were no differences for all inflorescence characters (inflorescence length, male zone length, sterile zone length and female zone length) among different concentrations of GA3 tested. On the contrary, significant differences among the tuber diameter classes for all inflorescence characteristics measured were markedly evident. Generally, sizes of almost all inflorescence characteristics increased with increasing tuber sizes. When considering vegetative characters, significant differences in the fresh and dry weights of bulbil stolon were found between treated and untreated tubers. Although there was a trend of increase in weights with increasing GA3 concentrations, but this was not statistically significant. Our results for R. vivipara showed the induction of flowering by GA3 only influence of flower initiation, but no effects on inflorescence and vegetation characteristics. The present study also revealed that large tuber size made more significant contributions to the prediction of flowering, and the magnitude of inflorescence characteristics
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