Variance Estimation for Systematic Designs in Spatial Surveys.

Show simple item record Fewster, Rachel en 2012-03-07T23:18:04Z en 2011 en
dc.identifier.citation Biometrics 67(4):1518-1531 2011 en
dc.identifier.issn 0006-341X en
dc.identifier.uri en
dc.description.abstract Summary In spatial surveys for estimating the density of objects in a survey region, systematic designs will generally yield lower variance than random designs. However, estimating the systematic variance is well known to be a difficult problem. Existing methods tend to overestimate the variance, so although the variance is genuinely reduced, it is over-reported, and the gain from the more efficient design is lost. The current approaches to estimating a systematic variance for spatial surveys are to approximate the systematic design by a random design, or approximate it by a stratified design. Previous work has shown that approximation by a random design can perform very poorly, while approximation by a stratified design is an improvement but can still be severely biased in some situations. We develop a new estimator based on modeling the encounter process over space. The new "striplet" estimator has negligible bias and excellent precision in a wide range of simulation scenarios, including strip-sampling, distance-sampling, and quadrat-sampling surveys, and including populations that are highly trended or have strong aggregation of objects. We apply the new estimator to survey data for the spotted hyena (Crocuta crocuta) in the Serengeti National Park, Tanzania, and find that the reported coefficient of variation for estimated density is 20% using approximation by a random design, 17% using approximation by a stratified design, and 11% using the new striplet estimator. This large reduction in reported variance is verified by simulation. en
dc.language ENG en
dc.publisher Wiley-Blackwell en
dc.relation.ispartofseries Biometrics en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. Details obtained from en
dc.rights.uri en
dc.title Variance Estimation for Systematic Designs in Spatial Surveys. en
dc.type Journal Article en
dc.identifier.doi 10.1111/j.1541-0420.2011.01604.x en
pubs.issue 4 en
pubs.begin-page 1518 en
pubs.volume 67 en
dc.rights.holder Copyright: The International Biometric Society en
dc.identifier.pmid 21534940 en
pubs.end-page 1531 en
dc.rights.accessrights en
pubs.subtype Article en
pubs.elements-id 253654 en Science en Statistics en
dc.identifier.eissn 1541-0420 en
pubs.record-created-at-source-date 2011-12-20 en
pubs.dimensions-id 21534940 en

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