1,721,001 research outputs found
Two-stage estimation of ungulate abundance in Maremma regional park using pellet group count
No full textThe estimation of biological population size at large scale by incomplete area surveys and replicated counts
No full textA two-stage estimation of biological population abundance is considered at large scale. In the first stage some area units are selected using without-replacement sampling, while in the second stage the estimation of abundance in each selected unit is performed through a suitable counting strategy. In order to account for the variability due to varying sizes. the use of unit size as an auxiliary variable is proposed at the design level by handling the inclusion probabilities of the units. at the estimation level by combining, the single abundance estimates as in the ratio and regression criteria, or at both levels. The results of an artificial comparison suggest the joint use of simple random sampling and ratio criterion. The asymptotic properties of the resulting estimator are derived when the estimation of abundances at the second stage is performed through the replicated use of the counting strategy. Copyright (C) 2002 John Wiley Sons, Ltd
Steady-state ranked set sampling for replicated environmental sampling designs
No full textIn replicated sampling protocols, each design replicate is independently and randomly placed onto the study
region. Subsequently, in order to estimate the objective parameter, the Horvitz–Thompson (HT) estimator is
usually considered for each design replicate and an overall estimator results from the average of the single
estimators. Obviously, the procedure gives rise to a sample of HTestimators under simple random sampling (SRS)
in such a way that the objective parameter is estimated by the corresponding sample mean. However, this
procedure is likely to produce uneven coverage of the region and hence a large variability of the overall estimator.
Therefore, to avoid such drawbacks, a quasi-systematic protocol for the design replicates is proposed. In this case,
the suggested procedure gives rise to a sample of HT estimators under steady-state ranked set sampling (SRSS)–a
generalization of well-known ranked set sampling (RSS)–so as to estimate the objective parameter by the
corresponding sample mean. The proposed method produces large efficiency gains and does not involve
supplementary sampling costs or extra field work
Ranked set sampling for replicated sampling designs
No full textIn practical ecological sampling studies, a certain design (such as plot sampling or line-intercept sampling) is usually replicated more than once. For each replication, the Horvitz-Thompson estimation of the objective parameter is considered. Finally, an overall estimator is achieved by averaging the single Horvitz-Thompson estimators. Because the design replications are drawn independently and under the same conditions, the overall estimator is simply the sample mean of the Horvitz-Thompson estimators under simple random sampling. This procedure may be wisely improved by using ranked set sampling. Hence, we propose the replicated protocol under ranked set sampling, which gives rise to a more accurate estimation than the replicated protocol under simple random sampling
Assessing Multivariate Normality on the "Worst" Sample Configuration
No full textA rotation procedure searching for the worst sample configuration is proposed when the hypothesis of multivariate normality is assessed by evaluating the univariate normality of each row of the scaled residual matrix.This procedure gives rise to multivariate normality test statistics which are invariant with respect to linear non-singular transformations of the sample data. An empirical power study with respect to selected alternative distributions demonstrates how the worst rotation procedure performs better than the rotation procedure proposed by Szkutnik
Variance decomposition in two-stage plot sampling: theoretical and empirical results
No full textThe statistical properties of two-stage plot sampling estimators of abundance are considered. In the first stage, some spatial units are selected over the whole study area according to a suitable sampling design, while in the second stage, the selected units are surveyed with floating plot sampling to estimate the abundance within. Some insights into the accuracy of the resulting estimators are obtained by splitting the saple variance into the first and secondstage components, while performance is empirically checked by means of a simulation study. Simulation results show that, in most situations, a relevant amount of the overall variance is due to the second stage sampling. © 2004 Kluwer Academic Publishers
Estimating population size by mark-resighting counts: theoretical considerations and empirical results
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