Multimodel Inference and Multimodel Averaging in Empirical Modeling of Occupational Exposure Levels

Empirical modeling of exposure levels has been popular for identifying exposure determinants in occupational hygiene. Traditional data-driven methods used to choose a model on which to base inferences have typically not accounted for the uncertainty linked to the process of selecting the final model. Several new approaches propose making statistical inferences from a set of plausible models rather than from a single model regarded as best. This paper introduces the multimodel averaging approach described in the monograph by Burnham and Anderson. In their approach, a set of plausible models are defined a priori by taking into account the sample size and previous knowledge of variables influent on exposure levels. The Akaike information criterion is then calculated to evaluate the relative support of the data for each model, expressed as Akaike weight, to be interpreted as the probability of the model being the best approximating model given the model set. The model weights can then be used to rank models, quantify the evidence favoring one over another, perform multimodel prediction, estimate the relative influence of the potential predictors and estimate multimodel-averaged effects of determinants. The whole approach is illustrated with the analysis of a data set of 1500 volatile organic compound exposure levels collected by the Institute for work and health (Lausanne, Switzerland) over 20 years, each concentration having been divided by the relevant Swiss occupational exposure limit and log-transformed before analysis. Multimodel inference represents a promising procedure for modeling exposure levels that incorporates the notion that several models can be supported by the data and permits to evaluate to a certain extent model selection uncertainty, which is seldom mentioned in current practic

Old gene duplication facilitates origin and diversification of an innovative communication system—twice

The genetic basis of parallel innovation remains poorly understood due to the rarity of independent origins of the same complex trait among model organisms. We focus on two groups of teleost fishes that independently gained myogenic electric organs underlying electrical communication. Earlier work suggested that a voltage-gated sodium channel gene (Scn4aa), which arose by whole-genome duplication, was neofunctionalized for expression in electric organ and subsequently experienced strong positive selection. However, it was not possible to determine if these changes were temporally linked to the independent origins of myogenic electric organs in both lineages. Here, we test predictions of such a relationship. We show that Scn4aa co-option and rapid sequence evolution were tightly coupled to the two origins of electric organ, providing strong evidence that Scn4aa contributed to parallel innovations underlying the evolutionary diversification of each electric fish group. Independent evolution of electric organs and Scn4aa co-option occurred more than 100 million years following the origin of Scn4aa by duplication. During subsequent diversification of the electrical communication channels, amino acid substitutions in both groups occurred in the same regions of the sodium channel that likely contribute to electric signal variation. Thus, the phenotypic similarities between independent electric fish groups are also associated with striking parallelism at genetic and molecular levels. Our results show that gene duplication can contribute to remarkably similar innovations in repeatable ways even after long waiting periods between gene duplication and the origins of novelty

Théâtre et pouvoir

Actes du IVe Colloque International sur le théâtre, domaines hispanique, hispano-américain et mexicain, en France, organisé les 8, 9 et 10 octobre 1998 à l’Université de Perpignan, par le Centre de Recherches Ibériques et Latino-américaines de l’Université de Perpignan