As in the case of Shewhart control charts, samples of size n = (n, + n 2) are taken, but in two phases. In the first phase, m items are inspected for two characterstics (x; y). If T for the mean vector of (x, y) is less than a certain W, sampling is terminated. If Tj1 > CL, (> W), an out-of-control condition is signaled; otherwise a second phase sample of n , units is drawn. Then Hotelling T2 for the entire sample is computed and used for a decision. The expressions to assess the BDS chart's performance are obtained by an appropriate axis rotation that transforms correlated variables into uncorrelated ones. (31 refs.)
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