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dc.contributor.authorSantos, José Antóniopt_PT
dc.contributor.authorGalante-Oliveira, Susanapt_PT
dc.contributor.authorBarroso, Carlospt_PT
dc.description.abstractThe current work presents an innovative statistical approach to model ordinal variables in environmental monitoring studies. An ordinal variable has values that can only be compared as “less”, “equal” or “greater” and it is not possible to have information about the size of the difference between two particular values. The example of ordinal variable under this study is the vas deferens sequence (VDS) used in imposex (superimposition of male sexual characters onto prosobranch females) field assessment programmes for monitoring tributyltin (TBT) pollution. The statistical methodology presented here is the ordered logit regression model. It assumes that the VDS is an ordinal variable whose values match up a process of imposex development that can be considered continuous in both biological and statistical senses and can be described by a latent non-observable continuous variable. This model was applied to the case study of Nucella lapillus imposex monitoring surveys conducted in the Portuguese coast between 2003 and 2008 to evaluate the temporal evolution of TBT pollution in this country. In order to produce more reliable conclusions, the proposed model includes covariates that may influence the imposex response besides TBT (e.g. the shell size). The model also provides an analysis of the environmental risk associated to TBT pollution by estimating the probability of the occurrence of females with VDS ≥ 2 in each year, according to OSPAR criteria. We consider that the proposed application of this statistical methodology has a great potential in environmental monitoring whenever there is the need to model variables that can only be assessed through an ordinal scale of values.pt_PT
dc.description.sponsorshipThis work was supported by the research project POCI/MAR/ 61893/2004 financed by the Portuguese Foundation for Science and Technology (FCT) and by the POCI 2010, co-financed by FEDER.pt_PT
dc.publisherRoyal Society of Chemistrypt_PT
dc.titleAn innovative statistical approach for analysing non-continuous variables in environmental monitoring: assessing temporal trends of TBT pollutionpt_PT
degois.publication.titleJournal of Environmental Monitoringpt_PT
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