A Note On Chromy’s Sampling Procedure

2020 ◽  
Author(s):  
Guillaume Chauvet
Keyword(s):  
Sampling Procedure ◽  
Sequential Method ◽  
Sampling Algorithm ◽  
Probability Sampling ◽  
Unequal Probability Sampling ◽  
Unequal Probability

Abstract Chromy (1979) proposed an unequal probability sampling algorithm, which is the default sequential method used in the SURVEYSELECT procedure of the SAS software. In this article, we demonstrate that Chromy sampling is equivalent to pivotal sampling. This makes it possible to estimate the variance unbiasedly for the randomized version of the method programmed in the SURVEYSELECT procedure.

Evaluation of sampling alternatives to quantify tree leaf area

2003 ◽  
Vol 33 (1) ◽  
pp. 82-95 ◽  
Author(s):  
H Temesgen
Keyword(s):  
Leaf Area ◽  
Poor Performance ◽  
Tree Crown ◽  
Two Stage ◽  
Zero Bias ◽  
Probability Sampling ◽  
First Order ◽  
Unequal Probability Sampling ◽  
Unequal Probability ◽  
Tree Leaf

High within- and among-tree crown variation have contributed to the difficulty of tree-crown sampling and single-tree leaf area (area available for photosynthesis) estimation. Using reconstructed trees, simulations were used to compare five sampling designs for bias, mean square error (MSE), and distribution of the estimates. All sampling designs showed nearly zero bias. For most sample trees, stratified random sampling resulted in the lowest MSE values, followed by ellipsoidal, two-stage systematic, simple random, and then by two-stage unequal probability sampling. The poor performance of two-stage unequal probability sampling can be ascribed to the unequal probability of inclusion of first-order branches and twigs.

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