bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison and Evaluation of Three Methods of Estimation of the Johnson Sb Distribution
Authors: Siekierski Krzysztof 
Published: May 2007

AbstractThre methods of estimating the parameters of the Johnson S6 distribution were tested by simulation. The maximum likelihood method, the method based on percentiles of a sample and the method based on moments of a transformed random variable were taken into consideration. Many sets of samples were generated differing in sizes and in the actual values of parameters, whereupon the parameters were estimated by the three methods. It was proved that if the sample is small or the skewness of the distribution is considerable, the maximum likelihood estimates can assume preposterous values. The method based on moments is recommended due to its simplicity and to the fact that the estimates, though usually biased, never assume absurd values.
Binary Longitudinal Data Analysis with Correlation a Function of Explanatory Variables
Authors: Darlington G. A. , Farewell V. T. 
Published: May 2007

AbstractWhen binary responses are observed over time, the dependence between observations for an individual must be considered. If the focus of a study is to identify the relationship between the binary response and a set of explanatory variables then the dependence between observations may also depend on the explanatory variables. An extension of a model where dependence is assumed to be constant will be considered. A model previously proposed for dependent binary responses will be revisited and a robust estimate of the variance‐covariance matrix of coefficient estimates will be suggested to provide estimates of standard errors. The results of simulation studies investigating the properties of coefficient estimates will be discussed. An example based on a study of the AIDS epidemic and intravenous drug use behaviour will be analyzed to illustrate the techniques.
New Better than Used and Other Concepts for a Class of Life Distributions
Authors: Rao B. Raja , Damaraju C. V. , Rao Pro F. B. Raja , Damaraju C. V. 
Published: May 2007

AbstractIt is well‐known that the inequalities used in the definition of the New Better than Used (N. B. U.) and the New Better than Used in Expectation (N.B.U.E.) concepts, see BARLOW and PROSCHAN (1965, 1975) become equalities if, and only if, the life length of an organism follows an exponential distribution. It is proved in the present paper that these inequalities also reduce to equalities for the class of life distributions that have the “setting the clock back to zero” property. Simple examples of these distributions include the exponential, the linear hazard exponential and the Gompertz distributions. The General Krane distributions (Krane 1963) belong to this class, as well as a recent model introduced by CHIANG and CONFORTI (1989) of a survival distribution in which the hazard rate is a function of the accumulated effect of an individual's continuous exposure to the toxic material in the environment and his biological reaction to the toxin absorbed.As a simple application of the result proved in the paper, the life expectancy of an organism at age γ0 involved in the N.B.U.E. concept is evaluated for the Gompertzian growth process and for the Chiang and Conforti model.
On a Class of Almost Unbiased Ratio Estimators
Authors: Biradar R. S. , Singh H. P. 
Published: May 2007

AbstractA class of almost unbiased ratio estimators for population mean σ is derived by weighting sample σ = (1/n) σ yi, ratio estimators σ and an estimator, σ (yi/xi). It is shown that NIETO DE PASCUAL (1961) estimator is a particular member of the class and an optimum estimator in the class (in the minimum variance sense) is identified. The results are illustrated through two numerical examples.
Effect of Selection on the Failure Rate Function
Authors: Suresh R. P. 
Published: May 2007

AbstractEffect of selection procedures such as truncation and genotypic selection, are studied using selection differentials. These studies are mainly restricted to the study of mean or percentiles of the characteristics of interest. However, in situations where improvement on longetivity is itself of interest, in addition to studying mean or percentiles, one may study the reliability characteristics such as Failure Rate, Mean Residual Life etc., of the lifetimes of individuals. In this paper, we study the effect of genotypic selection when the distribution function of the lifetime is governed by a single locus with 2 alleles. We compute the difference in the failure rate function from one generation to the next generation for different values of n, the number of generations. We also obtain the limiting values of the failure rate function as n and compute the number of generations required for the failure rate to reach a value close enough to the limiting failure rate function. We also consider an example in a two‐loci case and study the effect of selection on the failure rate function.
EM Algorithm for Segregation Analysis
Authors: Achuthan N. R. , Krishnan T. 
Published: May 2007

AbstractWe consider the problem of estimating segregation ratios in families based on ascertainment through affected children, formulate it as an incomplete problem and work out the EM algorithm for maximum likelihood estimation of segregation ratios. We treat both the cases of known and unknown ascertainment probability. We also derive expressions for the covariance matrix of the estimators suitable for computing along with the EM algorithm. We illustrate the method with an example, compare the computational effort with that required in using the scoring method and argue that the EM algorithm is simpler.
A Modification of the Edgeworth Approximation in the AR (1) Model
Authors: Liu Shu‐Ing , Su Chien‐Chou , Chien‐Chou Shu‐Ing Liu 
Published: May 2007

AbstractThis paper considers the sampling distribution problem of the least squares estimator for the parameter of some special autoregressive models. The Edgeworth approximation has been derived and a modification is proposed to improve its accuracy. Comparisons with the exact distribution and the so called Edgeworth‐B approximation have been discussed. The results show that the proposed approximation performs more accurately than the Edgeworth‐B approximation, especially, when models are close to the non‐stationary boundary.
Estimation in a Continuous State Space Branching Process
Authors: Kale Mohan , Deshmukh S. R. 
Published: May 2007

AbstractIn some biological studies it is impossible to count the total number of individuals, but the size of the population can be measured by it's weight or volume. The probability of extinction of such populations is an interesting parameter, e.g. in modelling of epidemics. In this paper, the estimation of extinction probability and the moments of the offspring distribution is studied and the asymptotic properties of the estimators are discussed.
Some Early Developments in Ratio Estimation
Authors: Sen A. R. 
Published: May 2007

AbstractJohn Graunt (1662) was the first to estimate the ratioy/xwhereyrepresents the total population andxthe known total number of registered births in the same areas during the preceding year.About 1765 Messance (Stephan, 1948) and Moheau (1778) published very carefully prepared estimates for France based on enumeration of population in certain districts and on the count of births, deaths and marriages as reported for the whole country. The districts from which the ratio of inhabitants to birth was determined only constituted a sample. Laplace (1786) prepared similar estimates in 1802 based on a two‐stage sampling plan.Recently Hansen and Hurwitz (1943) showed that the ratio estimate (yi/ni)XofYis unbiased where allxi's are known and thenthcluster is selected with p.p.s. More recently Hájek (1949), Lahiri (1951), Midzuno (1952) and Sen (1952) developed independently the sampling ofnclusters with p.p.s to the totals of the sizes of the sample clustersS(xi).Des Raj (1954) and Sen (1952, 1953) gave unbiased estimate of the variance of the estimator which was generally non‐negative for samples with smaller probabilities. Rao and Vijayan (1977) gave an unbiased estimator which is non‐negative for samples with larger probabilities. Hájek (1949) provided an almost unbiased estimator of the variance of the estimator.The paper discusses situations where Hájek's estimator of variance should be preferred to the Rao‐Vijayan estimator and vice versa.
On the Information Matrix of Exponential Mixture Models with Long‐term Survivors
Authors: Ghitany M. E. 
Published: May 2007

AbstractThe aim of this paper is to study the properties of the asymptotic variances of the maximum likelihood estimators of the parameters of the exponential mixture model with long‐term survivors for randomly censored data. In addition, we study the asymptotic relative efficiency of these estimators versus those which would be obtained with complete follow‐up. It is shown that fixed censoring at timeTproduces higher precision as well as higher asymptotic relative efficiency than those obtainable under uniform and uniform‐exponential censoring distributions over (0,T). The results are useful in planning the size and duration of survival experiments with long‐term survivors under random censoring schemes.
Estimation of Incidence from Age Wise Prevalence
Authors: Lamba I. M. S. , Singh Padam 
Published: May 2007

AbstractA method used by various researchers for estimation of incidence from prevalence data of a stable population for irreversible stable diseases has been validated. For this purpose a followup data was generated by life table distribution techniques with known mortality and incidence rates. The results show that the method as such cannot be used to estimate the true incidence from prevalence data of a crossectional study from stable population. The remote situation where the method will work has been discussed. A method has also been presented for situations where the known method fails i.e. duration of irreversible disease is less than the age of effected persons in a stable population.
Precision Estimation in Zelen's Single‐Consent Design
Authors: Matts J. P. , McHugh R. B. 
Published: May 2007

AbstractThe precision of a treatment contrast, as conventionally estimated in Zelen's Single‐Consent Design, is shown under randomization theory to be positively biased. The magnitude of this bias is demonstrated and a new statistic is derived which is a consistent estimator of the precision. Confidence interval estimation for the treatment contrast is also presented.
A Note on Quantile Estimation for Curtailed Experiments
Authors: Trajstman A. C. 
Published: May 2007

AbstractThere may be experiments where due to misadventure or logistic or ethical reasons final measurements on all experimental units cannot be obtained. If at least 50% of the final measurements have been taken estimates of the lower quantiles and the median can be obtained. For such curtailed experiments it is shown how quantiles, above those that can be estimated directly from the data set, can be estimated indirectly by exploiting a property of symmetric distributions. The performance of the indirect quantile estimator is compared with that of the direct quantile estimator and conditions for the indirect estimator to have smaller variance than the direct estimator are presented. It is also shown how the indirect estimator may be pooled with the direct estimator to obtain an improved estimate of the upper quantiles.When it cannot be assumed that the data come from a symmetric distribution transformations to symmetry may be performed and the indirect estimation technique used on the transformed data; back transformations then yield the estimates of the upper quantiles.
Randomization Analysis of Incomplete Data in Some Basic Designs
Authors: Dash S. P. , Bourghawi Suad M. , El‐Amaari Ali 
Published: May 2007

AbstractThe first two randomization moments of W = Tt.S.S./(Tt.S.S. + Error S.S.) are derived in case of (a) a completely randomized design with one observation missing using (I) Yates method of fitting constants and (II) the available observations only and in case of (b) a randomized block design in which one treatment is tested twice by mistake in a block and another treatment is not tested at all in that block using (I) all the available observations and (II) the data after deleting the observation due to the treatment tested by mistake in place of another treatment in a block.It is concluded that in each of the two cases for a completely randomized design, the F‐test is unbiased whereas in each of the two cases for a randomized block design the F‐test is in general not unbiased. However, if one treatment is tested twice by mistake in randomly chosen plots of some block, the F‐test is unbiased in both cases for a randomized block design.For a completely randomized design the F‐test is found to be a good approximation to the corresponding randomized test if N ≧ 80 in case (I) whereas in case (II) this approximation is of the same accuracy as that of case (I) if N ≧ 90. For a randomized block design it is seen that in case (I), the F‐test provides a good approximation to the corresponding randomization test if v≧r≧7 and in case (II) this approximation is of the same accuracy if r≧6 and r(v‐1)≧45.The analysis of several uniformity trial data shows that for values of “N” in the neighbourhood of 50 the agreement of the first two moments of “W” under the randomization theory and normal theory are reasonably close in all the four cases considered.
A Guide to Bivariate Ideas of Quantal Response Analysis, as Applied in Biometrics and Econometrics
Authors: Hutchinson T. P. 
Published: May 2007

AbstractA review is provided of the several bivariate generalisations of quantal response analysis that have appeared in the biometric and econometric literatures. There are three main types: (i) where a binary outcome is the result of two stimulants, and thus the bivariate distribution of the thresholds for response is relevant; (ii) where three or more alternative outcomes may arise from a single stimulant; and (iii) where the response itself is bivariate (i.e., two types of response may simultaneously be observed).
On Assessment of Bioequivalence for Drugs with Negligible Plasma Levels
Authors: Liu Jen‐Pei , Chow Shein‐Chung 
Published: May 2007

AbstractIn bioavailability studies, bioequivalence between drug products is usually determined based on some pharmacokinetic responses such as area under the blood or plasma concentration‐time curve and maximum concentration. For some drug products, however, we may have negligible plasma levels because their intended routes of administration. In this case, assessment of bioequivalence between drug products of this kind may be established using clinical endpoints such as therapeutic response and time to the onset of a therapeutic response. In this paper, we propose two procedures which modify the method of generalized estimating equations (Liang and Zeger, 1986) and the proportional hazard models for paired failure times to assess bioequivalence between two drug products under the structure of a standard two‐sequence, two‐period crossover design. An example concerning a bioequivalence trial for albuterol metered dose inhaler indicated for acute bronchospasm (Herson, 1991) is used to illustrate the proposed procedures.
Regression Models for Clinical Trials with Correlated Categorical Responses
Authors: Burnett R. T. , Shedden J. , Broekhoven L. 
Published: May 2007

AbstractRegression models for correlated categorical data are presented in which the covariance is a function of measured effects. The regression and covariance parameters are estimated by extended least square methods. A numerical example of a clinical trial comparing two antiemetic treatment regimes for patients receiving chemotherapy is given to illustrate the approach.
Incorporating Prior Beliefs in Treatment Allocation for Clinical Trials
Authors: Faraggi David , Reiser Benjamin 
Published: May 2007

AbstractRecently Faraggi and Reiser (1991) introduced a general dynamic treatment allocation scheme which incorporates the permuted block allocation procedure and the Begg Iglewicz procedure as special cases. A drawback of previous allocation methods is that they did not allow incorporation of prior knowledge of the relative importance of the prognostic factors. In this paper we extend our allocation model to incorporate the weighting of prognostic factors. A simulation study examines the effects of this procedure and an example of its implementation is given.
Configural Frequency Analysis as a Parametric Method for the Search of Types and Antitypes
Authors: Spiel Christiane , Von Eye Alexander 
Published: May 2007

AbstractThe article introduces Parametric Configural Frequency Analysis (CFA). It is argued that there are two types of parameters that can be of importance in CFA models. The first is effect parameters that are estimated from the data. This type of parameter is involved in almost all models of Classical, nonparametric CFA. The second type involves a priori or distributional parameters that can be used for estimation of expected frequencies. These parameters are specified a priori rather than estimated from data. A combination of models from Classical CFA and Parametric CFA is introduced as Semi‐Parametric CFA. Data examples illustrate the new CFA models in comparison with the Classical CFA. Interpretational issues are discussed.
Interaction Biases in Two‐Period Crossover Studies: A Modified Analysis to Test with More Sensitivity
Authors: Cleophas Ton J. M. 
Published: May 2007

AbstractThe two‐period crossover trial is considered the most powerful means of determining the efficacy of new drugs. However, this study design is frequently invalidated by treatment‐by‐period interaction. If, for example, the effect of the first treatment period carries on into the next one, then it influences the response to the latter period (carryover effect). A second problem is, that the standard approach (Hills‐Armitage analysis) for interaction bias has a low statistical sensitivity. The author recently described an alternative method entitled the clinical approach because it looks at the clinical performance of the separate treatment groups and not, as the standard approach, at the means of the groups. It may be hypothesized that this alternative approach is statistically more sensitive than the standard in situations where there is interaction in just one of the treatment groups. The present study uses two examples and a mathematical model. It shows that in case of single‐group interaction the clinical approach can, indeed, detect carryover effect at a 30% lower level than the standard. On the other hand, however, the standard approach does so even at a 40% lower level than the clinical in case of two‐group interaction. I conclude that one approach supplements the other and that they be used in future studies simultaneously.
Association, Symmetry and Diagonal Models for Occupational Mobility and Other Similar Square Contingency Tables Having Ordered Categorical Variables
Authors: Lawal H. Bayo 
Published: May 2007

AbstractThis paper examines various association, symmetry and “diagonal band” class models for both the British and Danish social mobility data. Composite models are also fitted to these data and the variety of models considered ensures that for most square tables, parsimonious models within the class of models examined in this study can always be found that will adequately describe such tables. The models considered in this study, which have been described in various forms by Goodman (1984), Upton (1985) and Tomizawa (1986) can suit most square tables having ordered classificatory variables. A model selection procedure is also examined.
Drug Addiction ‐ Pushers Generated from the Addicts
Authors: Billard L. , Dayananda P. W. A. 
Published: May 2007

AbstractThis work develops a model for the spread of drug addiction in a closed population of size N. The spread of addiction is considered as an epidemic process where the addicts mix homogeneously within the population. There is an additional group (or pushers) with whom the susceptibles interact, but who are generated from the addicts. State probabilities and moments are obtained for this stochastic process. An extension to a generalized model is also made.
Estimation of Difference of Population Means with Missing Observations
Authors: Bouza C. N. , Prabhu‐Ajgaonkar S. G. 
Published: May 2007

AbstractSampling strategies for estimating difference of population means are proposed. The original sample is fragmented into three subsamples. The use of a purposive device permits to measure only one of the variables in two samples. Bootstrap procedures are employed to evaluate distribution of the errors of estimators.
On the Frequency Distribution of a Product
Authors: Finney David J. 
Published: May 2007

AbstractBiometric interest often attaches to the product of two directly determined variables. In sugar production, for example, the yield of the desired commodity is the product of the total weight of cane or beet from unit area and the sugar content per unit weight. In crop and animal production, there are many analogous situations where experimental or other information may come from field plots or individual animals and the success of inferences or decisions is related to the frequency distribution of such a product. The voluminous published literature relating to frequency distributions appears to contain little that is directly relevant. It therefore seems worth placing on record results recently obtained for the third and fourth moments of a product in the simple case of both variables being Normally distributed.
The Discrete Distribution Used for the Log‐rank Test Can Be Inaccurate
Authors: Soper K. A. , Tonkonoh N. 
Published: May 2007

AbstractWhen the number of tumors is small, a significance level for the Cox‐Mantel (log‐rank) test Z is often computed using a discrete approximation to the permutation distribution. For j = 0,…, J let Nj(t) be the number of animals in group j alive and tumor‐free at the start of time t. Make a 2 × (1+J) table for each time t of the number of animals Rj(t) with newly palpated tumor out of the total Nj(t) at risk. There are a total of say K tables, one for each distinct time t with observed death or newly palpated tumor. The usual discrete approximation to the permutation distribution of Z is defined by taking tables to be independent with fixed margins Nj(t) and ΣRj(t) for all t.However, the Nj(t) are random variables for the actual permutation distribution of Z, resulting in dependence among the tables. Calculations for the exact permutation distribution are explained, and examples are given where the exact significance level differs substantially from the usual discrete approximation. The discrepancy arisis primarily because permutations with different Z‐scores under the exact distribution can be equal for the discrete approximation, inflating the approximate P‐value.
Bias in the Logarithm of Microbial Density Estimates from Serial Dilutions
Authors: Garthright Wallace E. 
Published: May 2007

AbstractThe bias in the most‐probable‐number (MPN) estimate of microbial densities derived from serial dilutions might be less important than it has appeared to be. For many purposes, bias in the logarithm of the MPN is more important than bias in the MPN, and the bias in the logarithm is much less. The lesser bias has been reduced by using the theorems of Salama, Koch, and Tolley. Formulas and tables are provided.