281 research outputs found
On an extension of the exponential-geometric distribution
No full textVarious statistical properties and reliability aspects of a two-parameter distribution with decreasing and increasing failure rate are explored; the model includes the exponential-geometric distribution [Marshall and Olkin, 1997. Biometrika 84, 641-652; Adamidis and Loukas, 1998. Statist. Probab. Lett. 39, 35-42] as a special case. Characterizations are given and the estimation of parameters is studied by the method of maximum likelihood. An EM algorithm [Dempster et al., 1977. J. R. Statist. Soc. B. 39, 1-38] is proposed for computing the estimates, and expressions for their asymptotic variances and covariances are derived. Numerical examples based on real data are included. (c) 2005 Elsevier B.V. All rights reserved.Statistics & Probability Letter
Leg extension test, semg and vibratory stimuli to assess functional recovery following knee joint surgery
No full textObjective: the purpose of this study was to introduce new procedure to determine the magnitude of functional recovery after knee surgery. Design: we compared the performance in the leg extension test and the response in the sEMG activity to vibration in the operated to the non-operated leg. Thirty-eight patients with knee operation and 14 healthy subjects participated in these experiments. Results: during leg extension test, the mechanical power of the operated leg showed a lower value (P<0.001) than the contralateral one, while no differences were noted in the sEMG activity. The sEMG activity during vibration treatment was higher in the operated compared to non-operated leg (P<0.001). It has been suggested that the reduced motility trigger functional adaptations that are exhibited via the vibration test. Conclusions: results of our study suggest that combination of vibration and sEMG recordings may detect the impairment as well as monitoring progress of the rehabilitation program
Ml Estimation in the Bivariate Poisson-Distribution in the Presence of Missing Values Via the Em Algorithm
No full textIn this paper we study the maximum likelihood estimation of parameters, of the bivariate Poisson distribution, by assuming a sample with a general pattern of missing observations and applying the EM algorithm (Dempster, Laird and Rubin, 1977). The application of the method is outlined in the complete-data estimation problem, considered by Holgate (1964), since the latter can be viewed as a special case of the missing-value problem studied here. The observed information matrix is also obtained by means of the EM algorithm (Louis, 1982) and numerical examples are presented. The application of Louis's method is found most appropriate and seen to produce remarkable acceleration in the convergence of the EM algorithm. Results of some interest, concerning the conditional distributions of Poisson variables, given particular sums of Poisson random variables are also established.Journal of Statistical Computation and Simulatio
A lifetime distribution with decreasing failure rate
No full textA two-parameter distribution with decreasing failure rate is introduced. Various properties are discussed and the estimation of parameters is studied by the method of maximum likelihood. The estimates are attained by the EM algorithm and expressions for their asymptotic variances and covariances are obtained. Numerical examples based on real data are presented. (C) 1998 Elsevier Science B.V. All rights reserved.Statistics & Probability Letter
Estimation in a truncated bivariate Poisson distribution using the EM algorithm
No full textAn EM algorithm (Dempster et al., 1977) is derived for the estimation of parameters of the truncated bivariate Poisson distribution with zeros missing from both margins. The observed information matrix is obtained and a numerical example is given where the convergence of the EM algorithm is accelerated by the methods of Louis (1982) and conjugate gradients (Jamshidian and Jennrich, 1993).Communications in Statistics-Theory and Method
Prescribed fire maintains host plants of a rare grassland butterfly
No full text© 2019, The Author(s). As grassland ecosystems transform globally due to anthropogenic pressures, improvements in our understanding of the effect of management on rare and threatened species in such landscapes has become urgent. Although prescribed fire is a very efficient tool for habitat restoration and endangered species management on fire-adapted ecosystems, the specific mechanisms underlying potential effects of burning on population dynamics of butterfly host plants are poorly understood. We analyzed a 12-year dataset (2004–2015), combining violet abundance, habitat physiognomy and fire history data from a fire-managed system, to determine factors influencing the spatiotemporal distribution and abundance of violets (Viola spp.), the host plants of the threatened eastern regal fritillary (Speyeria idalia idalia) butterfly. Our results demonstrate a critical role for fire in driving both presence and abundance of violets, suggesting management with prescribed fires can effectively promote butterfly host plants. In addition, we determined the character of habitats associated with violet presence and abundance, in particular a strong positive association with biocrusts. These results provide a roadmap for efficient site selection to increase the effectiveness of restoration efforts, including assessment of potential reintroduction sites for regal fritillary and other grassland butterflies and actions to promote the re-establishment of host plants in these sites
Investigation of a control scheme based on modified p-q theory for single phase single stage grid connected PV system
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