Nonparametric Simultaneous Tests for Location and Scale Testing: A Comparison of Several Methods

The two-sample location-scale problem arises in many situations like climate dynamics, bioinformatics, medicine, and finance. To address this problem, the nonparametric approach is considered because in practice, the normal assumption is often not fulfilled or the observations are too few to rely on the central limit theorem, and moreover outliers, heavy tails and skewness may be possible. In these situations, a nonparametric test is generally more robust and powerful than a parametric test. Various nonparametric tests have been proposed for the two-sample location-scale problem. In particular, we consider tests due to Lepage, Cucconi, Podgor-Gastwirth, Neuhäuser, Zhang, and Murakami. So far all these tests have not been compared. Moreover, for the Neuhäuser test and the Murakami test, the power has not been studied in detail. It is the aim of the article to review and compare these tests for the jointly detection of location and scale changes by means of a very detailed simulation study. It is shown that both the Podgor–Gastwirth test and the computationally simpler Cucconi test are preferable. Two actual examples within the medical context are discussed.     

Re-randomization tests as sensitivity analyses to confirm immunological noninferiority of an investigational vaccine: Case study

Here we present as case study how re-randomization tests were performed in two randomized, controlled clinical trials as sensitivity analyses, as recommended by the United States Food and Drug Administration in the context of adaptive randomization. This was done to confirm primary conclusions on immunological noninferiority of an investigational new fully liquid presentation of a quadrivalent cross-reacting material conjugate meningococcal vaccine (MenACWY-CRM), over its licensed lyophilized/liquid presentation. In two phase 2b studies (Study #1: NCT03652610; Study #2: NCT03433482), noninferiority of the fully liquid presentation of MenACWY-CRM to the licensed presentation was assessed and demonstrated for immune responses against meningococcal serogroup A (MenA), the only vaccine component modified from lyophilized to liquid in the new presentation. The original vaccine assignment algorithm, with a minimization procedure accounting for center or center within age strata, was used to re-randomize participants belonging to the fully liquid and licensed vaccine groups while keeping antibody responses, covariates and entry order as observed. Test statistics under re-randomization were generated according to the ANCOVA model used in the primary analysis. To confirm immunological noninferiority following re-randomization, the corresponding p-values had to be <0.025. For both studies and all primary objective evaluations, the re-randomization p-values were well below 0.025 (0.0004 for Study #1; 0.0001 for the two co-primary endpoints in Study #2). Re-randomization tests performed to comply with a regulatory request confirmed the primary conclusions of immunological noninferiority for the MenA of the fully liquid compared to the licensed vaccine presentation.     

The Redistributive Effects of the Tax Wedge in Italy

Abstract. This paper presents an original data set of microdata on the tax wedge in Italy, obtained by using the microsimulation model ITAXMOD, developed at ISPE (Institute for Studies on Economic Planning). These data are used to measure the components of the tax wedge and their burden on the total cost of labour at the individual level. The results have been aggregated across income brackets, socio-economic groups and sectors of employment. These data are the necessary preliminary input for any redistributive analysis and in addition they make the available data for Italy comparable with those of other countries. Scant attention has been paid up to now to the redistributive aspects of the tax wedge, since most analyses are based on the income of the “average production worker” which is far from an ideal standard for comparison. The computation of the tax wedge for different brackets of total labour cost has been explored in two ways. The first is related to the differing weights of the components of the tax wedge on cost of labour and no particular hypothesis has been made about the incidence of these components. The results show that the burden of personal income taxation and of social security contributions is very high even for wage-earners in the lowest brackets (in 1992, the estimated tax wedge is more than 44% of total labour cost even in the second decile of the labour cost). That might discourage both labour supply and labour demand across the entire spectrum of deciles of cost of labour. The second line of research studies the incidence of personal income taxes and employees' social security contributions on gross earnings, under the maintained hypothesis that these two components of the tax wedge are shouldered by the employees.