Sampling variance in sale lots and its influence on test precision [wool]
1993
Russell, B.C. | Cottle, D.J. (New South Wales Univ., Kensington (Australia). Dept. of Wool and Animal Science)
Some aspects of sampling raw wool sale lots are examined. In particular, the importance of within-bale variance to the design of sampling schedules and sampling precision is considered, and the most recent estimates of this parameter are reviewed. The estimate of within-bale variance of wool-base used in IWTO and Australian core-sampling standards is likely to be exceeded by around one-third of the Australian clip, especially non-fleece types. The importance of sampling variance to overall test precision is reviewed, and the effect of altering the sampling schedule on the precision of the combined certificate for consignments is determined. Increased sampling results in only a modest improvement in precision at both the lot and consignment level. The relevance of specifying a minimum sampling precision for sale lots is discussed, and it is argued that regular monitoring of all components of testing variance would be desirable.
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