Search results for "Additive model"
showing 8 items of 28 documents
Spatial Distribution and Abundance of Mesopelagic Fish Biomass in the Mediterranean Sea
2020
Mesopelagic fish, being in the middle of the trophic web, are important key species for the marine environment; yet limited knowledge exists about their biology and abundance. This is particularly true in the Mediterranean Sea where no regional assessment is currently undertaken regarding their biomass and/or distribution. This study evaluates spatial and temporal patterns of mesopelagic fish biomass in the 1994–2011 period. We do that for the whole Mediterranean Sea using two well-established statistical models, the Generalized Additive Model (GAM) and Random Forest (RF). Results indicate that the bathymetry played an important role in the estimation of mesopelagic fish biomass and in its …
Efficiency Bounds for Product Designs in Linear Models
1999
We provide lower efficiency bounds for the best product design for an additive multifactor linear model. The A-optimality criterion is used to demonstrate that out bounds are better than the conventional bounds. Applications to other criteria, such as IMSE (integrated mean squared error) criterion are also indicated. In all the cases, the best product design appears to perform better when there are more levels in each factor but decreases when more factors are included. Explicit efficiency formulas for non-additive models are also constructed.
Calf circumference is an independent predictor of mortality in older adults: An approach with generalized additive models.
2021
BACKGROUND There is a wide variation in the cutoff points of body mass index (BMI) and calf circumference (CC) , and it is necessary to assess their adequacy in predicting mortality, especially in the older adults in the community. This study aimed to investigate the association of low muscle mass and underweight with mortality in older adults, comparing different cutoff points. METHODS This was a prospective study that included 796 older adults, not institutionalized, from a Brazilian city. Generalized additive models (GAMs) were used to identify cutoff points for CC and BMI, which were compared with values available in the literature. Survival analysis using Cox regression models was used…
Tracking management-related water quality alterations by phytoplankton assemblages in a tropical reservoir
2015
Water quality improvement and suppression of cyanobacterial blooms were planned in a eutrophic reservoir in southern China through ecological engineering measures from 2006 to 2011. This consisted in (i) a hydraulic resetting of inflows and outflows to increase the distance between inlet and outlet and the water residence time in the reservoir, and in (ii) the installation of floating frames hosting wetland vegetation to promote an alteration in phytoplankton composition. The environmental changes were therefore followed through the analysis of biotic responses in phytoplankton assemblages. Ecological engineering was effective in reducing phytoplankton total biomass, in re-establishing more…
A comparison of nonparametric methods in the graduation of mortality: Application to data from the Valencia Region (Spain)
2006
[EN] The nonparametric graduation of mortality data aims to estimate death rates by carrying out a smoothing of the crude rates obtained directly from original data. The main difference with regard to parametric models is that the assumption of an age-dependent function is unnecessary, which is advantageous when the information behind the model is unknown, as one cause of error is often the choice of an inappropriate model. This paper reviews the various alternatives and presents their application to mortality data from the Valencia Region, Spain. The comparison leads us to the conclusion that the best model is a smoothing by means of Generalised Additive Models (GAM) with splines. The most…
Combined statistical and mechanistic modelling suggests food and temperature effects on survival of early life stages of Northeast Arctic cod (Gadus …
2015
Abstract Understanding the causes of the large interannual fluctuations in the recruitment to many marine fishes is a key challenge in fisheries ecology. We here propose that the combination of mechanistic and statistical modelling of the pelagic early life stages (ELS) prior to recruitment can be a powerful approach for improving our understanding of local-scale and population-scale dynamics. Specifically, this approach allows separating effects of ocean transport and survival, and thereby enhances the knowledge of the processes that regulate recruitment. We analyse data on the pelagic eggs, larvae and post-larvae of Northeast Arctic cod and on copepod nauplii, the main prey of the cod lar…
Do Saharan Dust Days Carry a Risk of Hospitalization From Respiratory Diseases for Citizens of the Canary Islands (Spain)?
2021
Background: Saharan dust meets the Canary Islands at the beginning of its westward path across the North Atlantic, exceeding the European daily levels for PM10; for this reason, their two provincial capital cities, constitute optimal sites where to evaluate the health effects of this natural event. Objectives: To assess the short-term association between Saharan Dust Days (SDDs) and respiratory morbidity in the two capital cities. Methods: We carried out a time-series analysis with daily emergency hospital admissions due to all respiratory system diseases, chronic obstructive pulmonary disease (COPD) and asthma between 2001 and 2005, assessing the independent effect of SDDs, defined accordi…
Non-linear regional weather-growth relationships indicate limited adaptability of the eastern Baltic Scots pine
2021
Abstract Under changing climate, temporal and spatial stability (stationarity) of growth responses of trees to weather and climate, which has often been presumed without explicit testing, is crucial for prediction of productivity and sustainability of forests. However, considering evolutionary adaptation of tree populations to wide spatiotemporal ecological gradients, extrapolation of linear responses, which could be observed in limited parts of the gradients (certain locality), can result in biased results. Accordingly, the plasticity of responses of tree-ring width of the eastern Baltic populations of Scots pine (Pinus sylvestris L.) to meteorological conditions across the regional climat…