Imputation using higher order moments of an auxiliary variable

In this article, we propose a new method of imputation that makes use of higher order moments of an auxiliary variable while imputing missing values. The mean, ratio, and regression methods of imputation are shown to be special cases and less efficient than the newly developed method of imputation, which makes use of higher order moments. Analytical comparisons show that the first-order mean squared error approximation for the proposed new method of imputation is always smaller than that for the regression method of imputation. At the end, the proposed higher order moments-based imputation method has been applied to a real dataset.     

Non-native plant species integrate well into plant-pollinator networks in a diverse man-made flowering plant community

Urban Ecosystems - Urban green areas offer diverse flower resources for pollinators. Yet, the role of non-native plant species in local plant-pollinator networks is understudied. We explored the...     

Contemporaneous and Intertemporal Relationship Between the Consumption of Licit and Illicit Substances by Youth

Using a representative sample of the 1999 National School-based Youth Risk Behavior Survey, this study investigated the risky behavior of cigarette, alcohol, and marijuana consumption by underage students. The research analyzes the contemporaneous and intertemporal relationship between the use of these licit and illicit substances. Evidence of a gateway from cigarettes to marijuana was found; however, prior use of alcohol does not significantly increase the likelihood of currently using marijuana.     

Structural adjustment and family policy in Africa: Lessons from Sudan

The economic strategy pursued by a country profoundly influences the well-being of families. This article uses a social accounting model of the Sudanese economy to compare the effects of two alternative development strategies on growth, employment, and income distribution. The first strategy considered is a conventional growth-oriented strategy emphasizing irrigated, export-oriented agriculture and modern, capital-intensive industry; the second one is a traditional agriculture-led development (TALD) strategy focused on enhancing equity and improving family nutrition by expanding food production. The study's findings for Sudan demonstrate that there is no necessary trade-off between growth and equity. The TALD strategy fosters income growth for the most vulnerable families while simultaneously maximizing aggregate growth. It also holds the prospect of enhancing family equity and increasing access to traditional institutions that provide support to families.World BankHer research interests encompass issues related to poverty and inequality in developing countries. She received her Ph.D. from Cornell University.Before joining the World Bank, he was a visiting scholar at the University of Connecticut and acting head of the Department of Econometrics, University of Khartoum, Khartoum, Sudan. His research interests span development economics (growth, poverty, and equity), public finance, and economic transition in Eastern Europe. He received his Ph.D. from the University of Pittsburgh.     

Does Gender Matter?

In this article we explore gender differences in opinion regarding controversial social issues. The issues we selected are: attitudes toward African Americans, Jews, Muslims, Affirmative Action, abortion, and gays and lesbians. This selection is based on the importance of these issues in public debate and electoral politics. A number of these issues, mainly those related to opinions toward religious and racial groups, reflect the development of the American society and draw lines of possible disagreements and social cleavages. Our purpose is to draw attention to an important factor in determining public opinion toward these issues. We aim to explore issues where gender makes a clear difference, where it does not only hold an important role as other factors such as race and political affiliation, and where considerations of gender need to be combined with other personal attributes in order to understand their real impact. These highlights are intended to shed light on the role of gender in social issues as well as understanding these issues from a perspective that includes gender as a dimension in opinion making.     

Estimation of the common scale of several shifted exponential distributions with unknown locations

We consider the estimation of the common scale parameter of two or more independent shifted exponential distributions with unknown locations. Under a large class of bowl-shaped loss functions, the best location-scale in-variant estimator is shown to be inadmissible. A class of improved estimators is derived. Some numerical results are presented to show the magnitude of risk reduction.     

Likelihood ratio tests for covariance hypotheses generating commutative quadratic subspaces

We show that the likelihood ratio (LR) tests, for covariance hypotheses in multivariate normal models, take the form of a product of powers of independent beta variates whenever the covariance matrices generate a commutative quadratic subspace (CQS), See Seely (1971), under both the model and the hypothesis.     

Piecewise deterministic Markov processes applied to fatigue crack growth modelling

In this paper, we use a particular piecewise deterministic Markov process (PDMP) to model the evolution of a degradation mechanism that may arise in various structural components, namely, the fatigue crack growth. We first derive some probability results on the stochastic dynamics with the help of Markov renewal theory: a closed-form solution for the transition function of the PDMP is given. Then, we investigate some methods to estimate the parameters of the dynamical system, involving Bogolyubov's averaging principle and maximum likelihood estimation for the infinitesimal generator of the underlying jump Markov process. Numerical applications on a real crack data set are given.