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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Record number 419846
Title Expert elicitation of the variogram
Author(s) Truong, N.P.; Heuvelink, G.B.M.; Gosling, J.P.
Source In: Pedometrics 2011 - Innovations in Pedometrics; Book of abstracts, August 30 - September 2, 2011, Prague, Czech Republic. - Prague : Czech University of Life Sciences - ISBN 9788021321953 - p. 48 - 48.
Event Prague : Czech University of Life Sciences - ISBN 9788021321953 Pedometrics 2011, 2011-08-30/2011-09-02
Department(s) Land Dynamics
PE&RC
Publication type Abstract in scientific journal or proceedings
Publication year 2011
Abstract Expert elicitation of the variogram P. Truong, G.B.M. Heuvelink, J.P. Gosling gerard.heuvelink@wur.nl Wageningen University, Department of Environmental Sciences, PO Box 47, 6700 AA Wageningen, Netherlands The variogram is the key instrument of geostatistics. Estimation of the variogram typically relies on a sufficiently large number of observations of the target variable. However, budget constraints may cause that a too sparse data set is used to estimate the variogram, which will impair the subsequent geostatistical analysis. In some cases it may even be impossible to collect observations to estimate the variogram, such as when in scenario studies the spatial variability of a variable defined in the future is to be assessed. In addition, prior information about the variogram may also be very useful to design an optimal sampling scheme in field surveys and in Bayesian geostatistics. It is, therefore, sensible to explore approaches to estimate the variogram other than through a structural analysis of observations. In this paper we explore how the variogram can be elicited from experts. Experts can be very knowledgeable about the spatial variability of target variables, but directly asking experts about the nugget, sill, range and shape of the variogram may not be sensible because many experts are not familiar with these concepts. The variogram is typically estimated by the average squared increments of the target variable over various lags, but robust estimation of the variogram uses the median of the absolute differences of the target variable over distances. Statistical expert elicitation is well developed to extract the median of uncertain quantities from experts. Thus, the median of the absolute increment is a sensible target quantity of the elicitation procedure. We developed an expert elicitation methodology on this principle, by eliciting the median for multiple separation distances and fitting a variogram. First, a protocol of a well-structured elicitation procedure was designed. Next a web-based tool for online elicitation was built that is composed of three main components: (1) web-GIS interface for elicitation and feedback, (2) statistical calculation and mathematical aggregation to merge the opinions of multiple experts and (3) database management. The prototype was tested and evaluated in a case study on elicitation of the variogram of soil pH. The evaluation showed that the online elicitation tool is satisfactory, although currently it is only a prototype that needs to be further developed.
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