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An Improvement on the Papadakis Covariate to Account for Spatial Variation

Girma Taye and Peter Njuho
Journal of Agricultural, Biological, and Environmental Statistics
Vol. 12, No. 3 (Sep., 2007), pp. 397-413
Stable URL: http://www.jstor.org/stable/27595650
Page Count: 17
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
An Improvement on the Papadakis Covariate to Account for Spatial Variation
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Abstract

The Papadakis covariate is commonly used to account for spatial variation in agricultural field experiments. However, it is calculated from the observed yield, and is affected by unexpected land discontinuity. To address this problem, we propose two extensions. First, we introduce a kriged residual and the kriged Papadakis residual, are discussed. The second extension is a modification of the conventional Papadakis covariate that assigns equal weight to neighboring plots, regardless of their distance from the point of interest. The proposed covariate (a modified Papadakis covariate) assigns different weights to plot yield according to their spatial position. The proposed extensions are compared to the conventional Papadakis covariate using field data from Ethiopia. Simulations were conducted to evaluate the performance of these covariates. The number of neighbors needed to compute the proposed covariate are determined by the range of the variogram.

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