Heteroscedasticity irrelevance when testing means difference

Peer Reviewe

Atribuir un significado a la matemática a través de la visualización

En el artículo se analiza la utilización de diagramas visuales en la resolución de problemas y su efecto sobre el significado que se atribuye a la matemática. En el trabajo se presta atención a la interacción de tres perspectivas -sociológica, cultural y cognitiva-, desde las cuales se han desarrollado investigaciones diversas sobre visualización.Some important aspects on the use of visualization during problem solving processes and its effect on giving signifi cance to mathematics are analized in this paper. The research presented here highlights the interaction among three different backgrounds supporting actual investigations on visualization: sociological, cultural and cognitive

Promoting the development of the academic path through the National System of Researchers. A first attempt at evaluation

Mexico is an OECD member country that historically has allocated less than half a per cent of its gross domestic product to spend on research and experimental development. The purpose of this paper is to evaluate the country's science and technology policy through its main program, the National System of Researchers (SNI), an attempt made for the first time. The results obtained make it possible to see whether the SNI has succeeded in improving research in Mexico. The authors also look at whether the program provides ways of improving and strengthening the science policy model adopted by Mexico and whether it could be extended and/or introduced into other nearby countries with levels of development or characteristics similar to those of Mexico

Heteroscedasticity irrelevance when testing means difference

Heteroscedasticity produces a lack of type I error control in Studentâs t test for difference between means. Pretesting for it (e.g., by means of Leveneâs test) should be avoided as this also induces type I error. These pretests are inadequate for their objective: not rejecting the null hypotheses is not a proof of homoscedasticity; and rejecting it may simply suggest an irrelevant heteroscedasticity. We propose a method to establish irrelevance limits for the ratio of variances. In conjunction with a test for dispersion equivalence, this appears to be a more affordable pretesting strategy

Carryover negligibility and relevance in bioequivalence studies

The carryover effect is a recurring issue in the pharmaceutical field. It may strongly influence the final outcome of an average bioequivalence study. Testing a null hypothesis of zero carryover is useless: not rejecting it does not guarantee the non-existence of carryover, and rejecting it is not informative of the true degree of carryover and its influence on the validity of the final outcome of the bioequivalence study. We propose a more consistent approach: even if some carryover is present, is it enough to seriously distort the study conclusions or is it negligible? This is the central aim of this paper, which focuses on average bioequivalence studies based on 2×2 crossover designs and on the main problem associated with carryover: type I error inflation. We propose an equivalence testing approach to these questions and suggest reasonable negligibility or relevance limits for carryover. Finally, we illustrate this approach on some real datasets

Verificación de supuestos en las pruebas de comparación de medias. Una revisión.

La validez de la prueba t de Student para determinar la existencia de diferencias significativas entre medias está limitada al cumplimiento de los supuestos de normalidad y homocedasticidad. El presente trabajo recopila los resultados de investigaciones que muestran que cuando estos supuestos se verifican mediante otros test de hipótesis tradicionales (por ejemplo, el test F o el test de Levene para la homoscedasticidad; tests de bondad de ajuste a una distribución normal…) existe un alto riesgo de cometer un error tipo I, además de la existencia de dificultades teóricas. Por otra parte cuando los supuestos se verifican mediante un enfoque de equivalencia con adecuados intervalos de irrelevancia, estos riesgos quedan mejor controlados, por lo que se recomienda el uso de este enfoque en lugar del tradicional, el cual se desaconseja. Se presentan los avances realizados en este tipo de estudios así como sugerencias de posibles desarrollos futuros en esta línea

An equivalence test between features lists, based on the Sorensen-Dice index and the joint frequencies of GO term enrichment

Background: In integrative bioinformatic analyses, it is of great interest to stablish the equivalence between gene or (more in general) feature lists, up to a given level and in terms of their annotations in the Gene Ontology. The aim of this article is to present an equivalence test based on the proportion of GO terms which are declared as enriched in both lists simultaneously. Results: On the basis of these data, the dissimilarity between gene lists is measured by means of the Sorensen-Dice index. We present two flavours of the same test: One of them based on the asymptotic normality of the test statistic and the other based on the bootstrap method. Conclusions: The accuracy of these tests is studied by means of simulation and their possible interest is illustrated by using them over two real datasets: A collection of gene lists related to cancer and a collection of gene lists related to kidney rejection after transplantation

On equivalence and bioequivalence testing

Equivalence testing is the natural approach to many statistical problems. First, its main application, bioequivalence testing, is reviewed. The basic concepts of bioequivalence testing (2×2 crossover designs, TOST, interval inclusion principle, etc.) and its problems (TOST biased character, the carryover problem, etc.) are considered. Next, equivalence testing is discussed more generally. Some applications and methods are reviewed and the relation of equivalence testing and distance-based inference is highlighted. A new distance-based method to determine whether two gene lists are equivalent in terms of their annotations in the Gene Ontology illustrates these ideas. We end with a general discussion and some suggestions for future research.Peer Reviewe

Statistical methods for quality equivalence of topical products. 0.5 mg/g betamethasone ointment as a case-study

This study examines the statistical implications, and their possible implementation, of the "Draft guideline on quality and equivalence of topical products" issued by the European Medicines Agency in 2018, with particular focus on the section devoted to quality equivalence of physical properties. A new confidence interval to conduct the quality equivalence test and a way to cope with the multiplicity of quality parameters are presented and discussed. As an example, the results and the statistical analysis of a study on betamethasone 0.5 mg/g ointment are presented. It is suggested that the equivalence limits proposed in the draft guideline are overly strict: It is as diffcult to declare quality equivalence between two packaging formats of the same reference product as to declare quality equivalence between the reference and the test product