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Several European countries make crop surveys on area frame with an aligned systematic sampling of squared segments. Crop area estimates are obtained with standard formulae for random sampling, without using the spatial structure of the sample. This estimates a standard error larger than the error actually made. Taking as clusters the set of segments with the same relative position in a block, gives lower but very unstable variances. A more stable variance estimate can be computed by repeated random permutations of the sample segments in each block before building up the clusters. There is a moderate variance reduction when no stratification has been performed. If the sample is stratified and the cluster estimator is applied in each stratum, the variances seem to be less unstable.

Additional information

Authors: FUENTES M, University of Valladolid, Department of Statistics (ES);GALLEGO F J, JRC Ispra (IT)
Bibliographic Reference: Paper presented: Sixth Kansas State University Conference on Applied Statistics in Agriculture, Manhattan (US), April 24-26, 1994
Availability: Available from (1) as Paper EN 38194 ORA
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