Accurate Estimation of Count Totals Using Ratio Estimators

Article

Mullenix, Paul   (1990, ASQC)   Harris Semiconductor

Journal of Quality Technology    Vol. 22    No. 4
QICID: 11271    October 1990    pp. 277-282
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Article Abstract

Estimating the count of a large number of parts with both speed and accuracy is a typical problem in a wide range of manufacturing industries. A common method used to count a large lot of parts is with a ratio estimator in which the weight of the total lot is divided by the weight per unit obtained from a sample. Automatic count machines are frequently used to perform these weighing and estimation operations. We address the accuracy of count estimation using a ratio estimator by showing how to choose sample sizes for estimating the true count to within some specified bound with high probability. Tables of required sample sizes for single and multiple sampling schemes are provided along with an example of counting parts from the integrated circuit industry. Finally, a method of control charting on the counting process is presented.

Keywords

Estimation


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