1,721,381 research outputs found
Design-based methodological advances to support national forest inventories: a review of recent proposals
Full text linkThe aim of this paper is to give an overview of some recent proposals to support national forest inventories. The reviewed literature is strictly of design- based nature, i.e., uncertainty only stems from the sampling scheme actually adopted in the survey, rather than being assumed or modeled as in model- based approaches. National forest inventories are viewed as two-phase sample surveys to estimate at the same occasion the extent of the continuous population of points constituting the forest cover and the total of a forest attribute (e.g., volume or biomass) in the discrete population of trees for several forest types and/or administrative districts. The first phase is performed from remote sensing imagery while the second phase is performed on the field, possibly adopting the information acquired in the first phase as auxiliary information. A novel methodology is adopted based on Monte Carlo integration methods, which leads to a very general estimation strategy. Some recent proposals are considered in which remote sensing information acquired in the first phase is used to assess some physical characteristics of non-forest resources, such as woodlots, tree-rows and isolated trees outside the forest without additional field work. Finally, a new proposal is discussed in which canopy height from laser scanning is adopted as auxiliary information to recover missing data occurring when some sampled points cannot be reached because of hazardous terrain
Acoustic and visual pacesetter influence on the energy expenditure in a cycling exercise
No full textBACKGROUND: The aim of this study was to evaluate the effects of acoustic and visual pacesetters on the energy expenditure in a steady state 30-minute long cycling. METHODS: Eighteen healthy male subjects (age 27.6±4.59 years; height 1.78±0.07 m; body mass 80.1±7.85 kg) performed a 30-minute submaximal exercise at a constant workload on a cycle ergometer. The imposed workload required a metabolic expenditure corresponding to 70% of ventilatory threshold for each subject. Energy expenditure - expressed as a caloric equivalent relative to the total net oxygen consumption during exercise - was evaluated using three conditions: control (CT), no external pacesetter; acoustic (AT), listening to rhythmic acoustic stimuli at 120 beat per minute; and visual (VT), seeing footage consisting of eight different images in a looped sequence at 120 frames per minute. RESULTS: All measured parameters qualified the exercise as requiring mainly an aerobic metabolism, showing no pain and no fatigue. AT and VT energy expenditure (5.0±0.44 and 4.9±0.39 MET respectively) were significantly lower compared to CT (5.5±0.49 MET), while no difference between AT and VT were recognized. CONCLUSIONS: This study confirmed the ergogenic effect of the acoustic pacesetter on a 30-minute steady state rhythmic exercise. Novelty is that the visual pacesetter too was able to increase the mechanical efficiency as the same manner than the acoustic one. The present setting adopting visual pacesetter could be used in special categories, such as the deaf or in innovative technological tools as head-mounted display devices
Design-based estimation of mark variograms in forest ecosystem surveys
No full textMark variograms are widely adopted in forest ecosystem studies for analyzing spatial interaction among trees. Inference on mark variograms can be performed under a model-dependent perspective (ergodic variograms) or under a deterministic perspective (non-ergodic variograms). A simple and workable definition of non-ergodic mark variogram is introduced based on distances between pairs of trees distinguished by distance classes. Design-based estimators of mark variogram values are proposed as the ratio of two Horvitz-Thompson estimators using replicated plots randomly located on the study area and making use of the inclusion probabilities of the pairs of trees. Jackknife estimators of their variances are considered. A simulation study is performed on a real forest stand to check the statistical performance of the proposed strategy. (c) 2019 Elsevier B.V. All rights reserved
Design-based mapping of tree attributes by 3P sampling
No full textThe estimation of individual values (marks) in a finite population of units (e.g., trees) scattered onto a survey region is considered under 3P sampling. For each unit, the mark is estimated by means of an inverse distance weighting interpolator. Conditions ensuring the design-based consistency of maps are considered under 3P sampling. A computationally simple mean squared error estimator is adopted. Because 3P sampling involves the prediction of marks for each unit in the population, prediction errors rather than marks can be interpolated. Then, marks are estimated by the predictions plus the interpolated errors. If predictions are good, prediction errors are more smoothed than raw marks so that the procedure is likely to better meet consistency requirements. The purpose of this paper is to provide theoretical and empirical evidence on the effectiveness of the interpolation based on prediction errors to prove that the proposed strategy is a tool of general validity for mapping forest stands
Harmonization of design-based mapping for spatial populations
Full text linkThe mapping of a survey variable throughout a continuum or for finite populations of units is usually performed from a model-dependent perspective. Nevertheless, when a sample of locations/units is selected by a probabilistic sampling scheme, the complex task of modelling can be avoided by using the inverse distance weighting interpolator and deriving the properties of maps in a design-based perspective. Conditions ensuring consistency of maps can be derived mainly based on some obvious assumptions about the pattern of the survey variable throughout the study region as well from the feature of the sampling scheme adopted to select locations/units. Nevertheless, in a design-based setting the totals of the survey variable for a set of domains partitioning the study region are commonly estimated by traditional estimators such as the Horvitz–Thompson estimator in the case of finite populations or the Monte-Carlo estimator in the case of continuous populations or by related estimators exploiting the information of auxiliary variables. That necessarily gives rise to different total estimates with respect to those achieved from the resulting maps as the sum of the interpolated values within domains. To obtain non-discrepant results, a harmonization of maps is here suggested, in such a way that the resulting totals arising from maps coincide with those achieved by traditional estimation. The capacity of the harmonization procedure to maintain consistency is argued theoretically and checked by a simulation study performed on some real population
Estimation of small woodlot and tree row attributes in large-scale forest inventories
No full textForest surveys performed over a large scale (e.g. national inventories) involve several phases of sampling. The first phase is usually performed by means of a systematic search of the study region, in which the region is partitioned into regular polygons of the same size and points are randomly or systematically selected, one per polygon. In most cases, first-phase points are selected and recognized in orthophotos or very high resolution satellite images available for the whole study area. Disregarding the subsequent phases, the first phase of sampling can be effectively adopted to select small woodlots and tree rows, in the sense that a unit is selected when at least one firstphase point falls within it. On the basis of such a scheme of sampling, approximately unbiased estimators of abundance, coverage and other physical attributes readily measurable from orthophotos (e.g. tree-row length) are proposed, together with estimators of the corresponding variances. A simulation study is performed in order to check the performance of the estimators under several distributions of units over the study area (random, clustered, spatially trended)
Design-based treatment of unit nonresponse in environmental surveys using calibration weighting
No full textUnit nonresponse is often a problem in sample surveys. It arises when the values of the survey variable cannot be recorded for some sampled units. In this paper, the use of nonresponse calibration weighting to treat nonresponse is considered in a complete design-based framework. Nonresponse is viewed as a fixed characteristic of the units. The approach is suitable in environmental and forest surveys when sampled sites cannot be reached by field crews. Approximate expressions of design-based bias and variance of the calibration estimator are derived and design-based consistency is investigated. Choice of auxiliary variables to perform calibration is discussed. Sen–Yates–Grundy, Horvitz-Thompson, and jackknife estimators of the sampling variance are proposed. Analytical and Monte Carlo results demonstrate the validity of the procedure when the relationship between survey and auxiliary variables is similar in respondent and nonrespondent strata. An application to a forest survey performed in Northeastern Italy is considered
Design-Based Maps for Finite Populations of Spatial Units
No full textThe estimation of the values of a survey variable in finite populations of spatial units is considered for making maps when samples of spatial units are selected by probabilistic sampling schemes. The single values are estimated by means of an inverse distance weighting predictor. The design-based asymptotic properties of the resulting maps, referred to as the design-based maps, are considered when the study area remains fixed and the sizes of the spatial units tend to zero. Conditions ensuring design-based asymptotic unbiasedness and consistency are derived. They essentially require the existence of a pointwise or uniformly continuous density function of the survey variable onto the study area, some regularities in the size and shape of the units and the use of spatially balanced designs to select units. The continuity assumption can be relaxed into a Riemann integrability assumption when estimation is performed at a sufficiently small spatial grain and the estimates are subsequently aggregated at a greater grain. A computationally simple mean squared error estimator is proposed. A simulation study is performed to assess the theoretical results. An application to estimate the map of wine cultivations in Tuscany (Central Italy) is considered
Eliminating nuisance parameters: two characterizations
No full textBayesian inference, finite additivity, integrated likelihood, measurable selection, nuisance parameter, statistical model, Primary 62A15, secondary 60A05,
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