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17 results on '"Tripathi, Ram C."'

1. A Closed Form Approximation of Moments of New Generalization of Negative Binomial Distribution

Author

Roy, Sudip, Tripathi, Ram C., and Balakrishnan, N.

Subjects
Mathematics - Statistics Theory, Statistics - Methodology
Abstract

In this paper, we propose a closed form approximation to the mean and variance of a new generalization of negative binomial (NGNB) distribution arising from the Extended COM-Poisson (ECOMP) distribution developed by Chakraborty and Imoto (2016)(see [4]). The NGNB is a special case of the ECOMP distribution and was named so by these authors. This distribution is more flexible in terms of the dispersion index as compared to its ordinary counterparts. It approaches the COM-Poisson distribution (Shmueli et al. 2005) [11] under suitable limiting conditions. The NGNB can also be obtained from the COM-Negative Hypergeometric distribution (Roy et al. 2019)[10] as a limiting distribution. In this paper, we present closed-form approximations for the mean and variance of the NGNB distribution. These approximations can be viewed as the mean and variance of convolution of independent and identically distributed negative binomial populations. The proposed closed-form approximations of the mean and variance will be helpful in building the link function for the generalized negative binomial regression model based on the NGNB distribution and other extended applications, hence resulting in enhanced applicability of this model., Comment: 14 pages, 1 figure

Published
2019

13. Regression to the Mean in Half-Life Studies.

Author

TEXAS UNIV AT SAN ANTONIO DIV OF MATHEMATICS AND COMPUTER SCIENCE, Tripathi, Ram C., TEXAS UNIV AT SAN ANTONIO DIV OF MATHEMATICS AND COMPUTER SCIENCE, and Tripathi, Ram C.

Abstract

Half-life studies of environmental contaminants in humans are restricted to only a few measurements per subject taken after the initial exposure, the initial dose is usually unknown, and subjects are included in the study only if their body burden is above a threshold C. The assumption of a one compartment first order decay model leads to a repeated measures linear model relating the logarithm of the biomarker with time, with the negative of the coefficient of time being the decay rate. The usual least-squares estimate of the decay rate is biased due to regression to the mean. In this report, based on the repeated measure linear model, unbiased estimates of the decay rate have been developed by the method of least-squares. This has been done for the two cases: (1) when there is no covariate (Report I) and (2) when there is a categorical covariate (Report II). The maximum likelihood estimator of the decay rate is developed (Report III) under the assumption that the logarithm of the concentration of the contaminant for the k time points of each subject has a truncated multivariate normal distribution with AR (1).

Published
1998

15. Parmacokinetics of 2,3,7,8-tertrachlorodibenzo-p-dioxin in Seveso adults and veterans of Operation Ranch Hand.

Author

Michalek, Joel E., Pirkle, James L., Needham, Larry L., Patterson Jr., Donald G., Caudill, Samuel P., Tripathi, Ram C., and Mocarelli, Paolo

Subjects
AGENT Orange, PHARMACOKINETICS, TETRACHLORODIBENZODIOXIN
Abstract

A combined analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) elimination in Seveso adults and Ranch Hand veterans found a period of fast elimination within the first 0.27 years after exposure in Seveso, followed by a period of slower elimination between 3 and 16.35 years from exposure. The mean TCDD elimination rate within the first 0.27 years after exposure among six adult males in the Seveso cohort was 2.0646 year[sup -1] (half-life = 0.34 years). The mean rate from 3 to 16.35 years was 0.1011 year[sup -1] (half-life = 6.9 years). The mean Ranch Hand elimination rate, 00924 year[sup -1] (half-life = 6.9 years), measured between 9 and 33 years after exposure, was significantly less than the Seveso mean in the first 0.27 years after exposure, but not significantly different from the Seveso mean between 3 and 16.35 years after exposure. The fast elimination within the first 0.27 years followed by a slower rate after 3 years is consistent with the expected pattern in a two-compartment open model, with a distribution phase of rapid elimination followed by a slower elimination phase. [ABSTRACT FROM AUTHOR]

Published
2002
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16. Maximum (Max) and Mid-P Confidence Intervals and p Values for the Standardized Mortality and Incidence Ratios.

Author

Kulkarni, Pandurang M., Tripathi, Ram C., and Michalek, Joel E.

Subjects
CONFIDENCE intervals, POISSON distribution, STATISTICAL hypothesis testing, MORTALITY, EPIDEMIOLOGY research methodology
Abstract

The authors present algorithms to compute the confidence interval for a Poisson parameter (λ) and the p value for testing the hypothesis that λ is equal to a constant, which can be used to make inferences about the standardized mortality ratio and the standardized incidence ratio. The p value and confidence interval always agree, despite the discrete nature of the Poisson distribution. The authors also give simple equations to compute numeric approximations of the confidence limits that do not require the use of any probability distributions. An example based on data arising from a study of cancer incidence is given. [ABSTRACT FROM PUBLISHER]

Published
1998
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17. The Survival of Human Enteric Viruses in Holding Ponds.

Author

TEXAS UNIV AT SAN ANTONIO CENTER FOR APPLIED RESEARCH AND TECHNOLOGY, Sagik,B P, Funderburg,Steven W, Moore,Barbara E, Tripathi,Ram C, Sorber,Charles A, TEXAS UNIV AT SAN ANTONIO CENTER FOR APPLIED RESEARCH AND TECHNOLOGY, Sagik,B P, Funderburg,Steven W, Moore,Barbara E, Tripathi,Ram C, and Sorber,Charles A

Abstract

The inactivation of Poliovirus I and Coxsackievirus B-3 was studied in model wastewater holding ponds. The ponds are constructed at cast concrete tanks 5 feet in diameter and 18, 30, 42 and 90 inches deep. Experiments were conducted using either settled wastewater (primary effluent) or wastewater that had undergone biological treatment and chlorine disinfection (final effluent). Results indicated that viral inactivation was more rapid during the warmer seasons, and in final effluent. The rate of viral inactivation was enhanced by the development of alkaline pH in holding ponds due to algal metabolism. Approximately 10% of the viruses added to the ponds was detected in the settled solids. The virions in the sediment portion of the ponds underwent inactivation less rapidly than those viruses in the water columns. (Author)

Published
1978

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