A COMPARISON OF THE IMPRECISE BETA CLASS, THE RANDOMIZED PLAY-THE-WINNER RULE AND THE TRIANGULAR TEST FOR CLINICAL TRIALS WITH BINARY RESPONSES

This paper develops clinical trial designs that compare two treatments with a binary outcome. The imprecise beta class (IBC), a class of beta probability distributions, is used in a robust Bayesian framework to calculate posterior upper and lower expectations for treatment success rates using accumulating data. The posterior expectation for the difference in success rates can be used to decide when there is sufficient evidence for randomized treatment allocation to cease. This design is formally related to the randomized play‐the‐winner (RPW) design, an adaptive allocation scheme where randomization probabilities are updated sequentially to favour the treatment with the higher observed success rate. A connection is also made between the IBC and the sequential clinical trial design based on the triangular test. Theoretical and simulation results are presented to show that the expected sample sizes on the truly inferior arm are lower using the IBC compared with either the triangular test or the RPW design, and that the IBC performs well against established criteria involving error rates and the expected number of treatment failures.     

Properties of generalized Levinson–Durbin–Whittle sequences

For a discrete time, second-order stationary process the Levinson–Durbin recursion is used to determine best fitting one-step-ahead linear autoregressive predictors of successively increasing order, best in the sense of minimizing the mean square error. Whittle [1963. On the fitting of multivariate autoregressions, and the approximate canonical factorization of a spectral density matrix. Biometrika 50, 129–134] generalized the recursion to the case of vector autoregressive processes. The recursion defines what is termed a Levinson–Durbin–Whittle sequence, and a generalized Levinson–Durbin–Whittle sequence is also defined. Generalized Levinson–Durbin–Whittle sequences are shown to satisfy summation formulas which generalize summation formulas satisfied by binomial coefficients. The formulas can be expressed in terms of the partial correlation sequence, and they assume simple forms for time-reversible processes. The results extend comparable formulas obtained in Shaman [2007. Generalized Levinson–Durbin sequences, binomial coefficients and autoregressive estimation. Working paper] for univariate processes.     

On the Order of Data Reductions by Ancillarity and by Sufficiency

In the context of frequentist inference there are strong arguments in favour of data reduction by both (a) conditioning on the most appropriate ancillary statistic and (b) restricting attention to a minimal sufficient statistic. However, significantly for the study of the foundations of frequentist inference, there are some examples in which the order of application of these data reductions has an important bearing on the statistical inference of interest. This paper presents a new simple example of this kind.     

Approximate and exact distributions of rank tests for balanced incomplete block designs

Judges rank k out of t objects according to m replic ations of abasic balanced incomplete block design with bblocks. In Alvo and Cabilio(1991),it is shown that the Durbin test, which is the usual test in this situation, can be written in terms of Spearman correlations between the blocks, and using a Kendall correlation, they generated a new statistic for this situation.This Kendall tau based statistic has a richer support than the Durbin statistic, and is at least as efficient.In the present paper,exact and simulation based tables are generated for both statistics, and various approximations to these null distributions are considered and compared.     

Impact of Canadian Postsecondary Education on Occupational Prestige of Highly Educated Immigrants

Cet article utilise les données provenant de l'Enquête longitudinale auprès des immigrants du Canada (ELIC) couvrant la période 2000‐2004 afin d'évaluer l'emploi à durée déterminée et la réussite professionnelle des immigrants récents qui, bien qu'ayant obtenu un diplôme universitaire dans leur pays d'origine, ont choisi de s'inscrire dans un établissement d'enseignement postsecondaire canadien. La principale conclusion de l'article est que la réussite professionnelle des immigrants très instruits est affectée par le choix de l'enseignement post‐secondaire au Canada, toutes catégories socio‐démographiques et conditions d'avant ou après migration confondues. Quatre années après leur arrivée au Canada, les immigrants occupent des emplois nettement moins prestigieux que ceux qu'ils avaient avant la migration. Les immigrants qui ont poursuivi des études universitaires au Canada atteignent des meilleurs résultats professionnels que les non‐participants ou ceux qui ont choisi un collège communautaire. Néanmoins, la majorité des immigrants très instruits n'ont pas réussi à retrouver leur profession. This paper uses data from the Longitudinal Survey of Immigrants to Canada covering the period 2000 to 2004 to assess short‐term employment and occupational attainment of recent immigrants who, despite having completed a university degree in their countries of origin, chose to obtain additional credentials at a Canadian postsecondary institution. The main finding of this paper is that occupational attainment of highly educated immigrants is affected by choice of postsecondary education in Canada regardless of differences in sociodemographic, premigration characteristics, and postmigration conditions. Four years after entry, immigrants worked in jobs with significantly lower occupational prestige than those held prior to migration. Immigrants who pursued a university education in Canada attained highest occupational outcomes when compared to nonparticipants and those who chose a community college pathway. Nevertheless, the majority of highly educated immigrants failed to gain entry to the professions.