The construction of the Beta Israel identity

Competing narrative discourses still define the early origins of the Beta Israel (Ethiopian Jews or black Jews of Ethiopia). A difficulty with reconstructing the past of Judaism in Ethiopia is that written records, though scarce, claim for themselves the 'unquestioned' role of narrating, controlling, containing and policing what can be said about the identities of the Beta Israel. This arrogance of written records is however constantly subverted by the oral sources of the history of the origin of the Beta Israel. The oral sources imply a multiplicity of versions of the same story, and their use in this article suggests that the question of the use of narrative discourse in attempting to name the identities of the Beta Israel in a context of social crisis is a process potentially subject to different interpretations in different historical periods.     

Can Africa Reduce Poverty by Half by 2015?

This article uses simulations to explore the possibility of halving the number of people in Africa living in extreme poverty by 2015. It shows that initial levels of inequality and per capita consumption determine the cumulative growth and reductions in inequality required to achieve this target, and finds that on average Africa needs only a relatively modest annual rate of growth in per capita household consumption, if inequality remains unchanged. The trade‐off between the two varies greatly among countries, and their policy choices are thus quite different: in some cases small changes in income distribution can have a large effect on poverty, while in others a strong focus on growth is the only viable option.     

Efficient Rank Regression with Wavelet Estimated Scores

We provide an estimate of the score function for rank regression using compactly supported wavelets. This estimate is then used to find a rank-based asymptotically efficient estimator for the slope parameter of a linear model. We also provide a consistent estimator of the asymptotic variance of the rank estimator. For related mixed models, the asymptotic relative efficiency is also discussed     

Comparing several exponential populations with more than one control

Suppose there are k ₁ (k ₁ ≥ 1) test treatments that we wish to compare with k ₂ (k ₂ ≥ 1) control treatments. Assume that the observations from the ith test treatment and the jth control treatment follow a two-parameter exponential distribution and , where θ is a common scale parameter and and are the location parameters of the ith test and the jth control treatment, respectively, i = 1, . . . ,k ₁; j = 1, . . . ,k ₂. In this paper, simultaneous one-sided and two-sided confidence intervals are proposed for all k ₁ k ₂ differences between the test treatment location and control treatment location parameters, namely , and the required critical points are provided. Discussions of multiple comparisons of all test treatments with the best control treatment and an optimal sample size allocation are given. Finally, it is shown that the critical points obtained can be used to construct simultaneous confidence intervals for Pareto distribution location parameters.     

Robust estimation and selection for single-index regression model

In this paper, we consider a single-index regression model for which we propose a robust estimation procedure for the model parameters and an efficient variable selection of relevant predictors. The proposed method is known as the penalized generalized signed-rank procedure. Asymptotic properties of the proposed estimator are established under mild regularity conditions. Extensive Monte Carlo simulation experiments are carried out to study the finite sample performance of the proposed approach. The simulation results demonstrate that the proposed method dominates many of the existing ones in terms of robustness of estimation and efficiency of variable selection. Finally, a real data example is given to illustrate the method.     

Bounded influence nonlinear signed‐rank regression

In this paper we consider weighted generalized‐signed‐rank estimators of nonlinear regression coefficients. The generalization allows us to include popular estimators such as the least squares and least absolute deviations estimators but by itself does not give bounded influence estimators. Adding weights results in estimators with bounded influence function. We establish conditions needed for the consistency and asymptotic normality of the proposed estimator and discuss how weight functions can be chosen to achieve bounded influence function of the estimator. Real life examples and Monte Carlo simulation experiments demonstrate the robustness and efficiency of the proposed estimator. An example shows that the weighted signed‐rank estimator can be useful to detect outliers in nonlinear regression. The Canadian Journal of Statistics 40: 172–189; 2012 © 2012 Statistical Society of Canada     

On the Choice of a Prior for Bayesian D-Optimal Designs for the Logistic Regression Model with a Single Predictor

The Bayesian design approach accounts for uncertainty of the parameter values on which optimal design depends, but Bayesian designs themselves depend on the choice of a prior distribution for the parameter values. This article investigates Bayesian D-optimal designs for two-parameter logistic models, using numerical search. We show three things: (1) a prior with large variance leads to a design that remains highly efficient under other priors, (2) uniform and normal priors lead to equally efficient designs, and (3) designs with four or five equidistant equally weighted design points are highly efficient relative to the Bayesian D-optimal designs.