Dynamics of buried seed population and seedling cohorts of two dominant weeds in a hill agroecosystem of the humid subtropics of India

Dynamics of the buried seeds and plant population of two dominant weeds, viz.,Emilia sonchifolia (Linn.) DC. andRichardsonia pilosa HBK were studied in the crop fields of Meghalaya, north-east India during radish and maize cropping and intervening fallow periods. The total buried seed population ofR. pilosa was always larger than that ofE. sonchifolia, but the germinable fraction was invariably greater in the latter. A major portion (39–41%) of the viable (germinable+dormant) seed population in both weeds was confined to the surface soil layer (0–5 cm). The viable seed population ofE. sonchifolia peaked during April, while that ofR. pilosa showed two peaks (during August and December). The survival pattern and half-lives of seedling cohorts showed, some differences in the two weed species, but both being summer annuals, their populations behaved in a similar manner by showing higher seedling recruitment (K) and survivorship (p) rates in the summer crop (maize) than in the winter crop (radish). However, the density of plants that could attain adulthood was significantly higher inE. sonchifolia thanR. pilosa which might have resulted in greater seed input of the former to the soil leading to its greater abundance in the crop fields. Supported by the University Grants Commission, New Delhi (Grants No. F. 3-37/87 SR II)     

The inclusion of minority groups in clinical trials: problems of under representation and under reporting of data

Objective: To evaluate the representation of minority groups in randomized control trials (RCTs), and the frequency with which this information is reported. Study Design: Reviewers collected data on the racial/ethnic composition of study samples from all RCTs published in six leading medical journals in 1999. Results: Of the 280 RCTs, most (204, 71.3%) provided no information on the race/ethnicity of participants. Of the 89 U.S.-based RCTs, 50 (56.1%) reported their minority distribution. Relative to other trials, those funded by the National Institute of Health (NIH) (n = 52) were more likely to report race/ethnicity data (55.8% vs. 23.7%; x2 = 20.9, p <_0.001) and to include nonwhite participants (13.5 % vs. 12.5%; x2=22.7, p<_0.001). Conclusion: Minority groups are currently under-represented in clinical trials. Information on the race and ethnicity of clinical trial participants is currently underreported in six leading medical journals. Reporting of minority group information was significantly better only in NIH funded trials, which also were more likely to include nonwhite participants. This suggests that mandatory reporting policies may have a positive effect on both reporting and representation.     

Preservation of Some Aging Properties and Stochastic Orders by Weighted Distributions

By assuming that a random variable X possesses an aging property, we provide conditions under which the corresponding weighted version X ₁, with weight function w ₁(·), would also possess this aging property. Similarly, by assuming that two random variables X and Y are ordered with respect to a stochastic order, we provide conditions under which the corresponding weighted versions X ₁ and Y ₂, with weight functions w ₁(·) and w ₂(·), respectively, preserve this stochastic ordering. We also point out fallacies in the similar results claimed by Jain et al. (1989 Jain , K. , Singh , H. , Bagai , I. ( 1989 ). Relations for reliability measures of weighted distributions . Commun. Statist. Theory Meth. 18 : 4393 – 4412 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) and Bartoszewicz and Skolimowska (2006 Bartoszewicz , J. , Skolimowska , M. ( 2006 ). Preservation of classes of life distribution and stochastic orders under weighting . Statist. Probab. Lett. 76 : 587 – 596 .[Crossref] , [Google Scholar]) and correct them.     

Estimation of Ordered Location Parameters: The Exponential Distribution

The problem of component wise estimation of ordered location parameters θ ₁ (θ ₁ ≤ θ ₂) of two independent exponential distributions is investigated. The scale parameters are assumed to be unequal but known. Independent random samples of unequal sample sizes are drawn from two populations and the estimators admissible among the mixed estimators of θ ₁ and θ ₂ are obtained. It is shown that the minimum risk estimators (MREs) of θ ₁ and θ ₂ without assuming θ ₁ ≤ θ ₂ are inadmissible when one does assume that θ ₁ ≤ θ ₂. The efficiencies of mixed estimators relative to MREs (without assuming θ ₁ ≤ θ ₂) are tabulated for equal sample sizes and equal scale parameters.     

Consistent estimation of regression coefficients in ultrastructural measurement error model using stochastic prior information

The problem of consistent estimation of regression coefficients in a multivariate linear ultrastructural measurement error model is considered in this article when some additional information on regression coefficients is available a priori. Such additional information is expressible in the form of stochastic linear restrictions. Utilizing stochastic restrictions given a priori, some methodologies are presented to obtain the consistent estimators of regression coefficients under two types of additional information separately, viz., covariance matrix of measurement errors and reliability matrix associated with explanatory variables. The measurement errors are assumed to be not necessarily normally distributed. The asymptotic properties of the proposed estimators are derived and analyzed analytically as well as numerically through a Monte Carlo simulation experiment.     

Families of neighbour designs and their analysis

Several methods of construction of generalised neighbour designs of equal and unequal block sizes are presented alongwith examples. Some methods for constructing neighbour designs of Rees are also given. The outline of analysis of generalised neighbour design has also been suggested.     

The mass class and teaching assistants: A case for discussion exercises

Sociology courses, particularly introductory courses, with 200 or more students are increasingly being offered in U.S. colleges and universities. Within the “mass class” structure, teaching assistants are often utilized to instruct students in smaller discussion sessions. This creates unique conditions of instruction for both professors and teaching assistants. For instance, professors are faced with coordinating teaching assistants’ activities, while teaching assistants need to develop skills relating to provoking discussion. Both must deal with effects of a hierarchy of instruction. After discussing these conditions we present structured classroom exercises that focus on sociological concepts typically presented in introductory courses to help teaching assistants create an engaging learning experience, attain teaching skills, and facilitate the professor’s coordination of instruction.     

Stochastic comparisons of multivariate frailty models

A multivariate frailty model in which survival function depends on baseline distributions of components and the frailty random variable is considered. Since misspecification in choice of frailty distribution and/or baseline distribution may affect the distribution of multivariate frailty model, using theory of stochastic orders, we compare multivariate frailty models arising from different choices of frailty distribution.