Abstract
In this article, we consider the T
2 chart with double sampling to control bivariate processes (BDS chart). During the first stage of the sampling, n
1 items of the sample are inspected and two quality characteristics (x; y) are measured. If the Hotelling statistic for the mean vector of (x; y) is less than w, the sampling is interrupted. If the Hotelling statistic
is greater than CL1, where CL1>w, the control chart signals an out-of-control condition. If
, the sampling goes on to the second stage, where the remaining n
2 items of the sample are inspected and
for the mean vector of the whole sample is computed. During the second stage of the sampling, the control chart signals an out-of-control condition when the statistic
is larger than CL2. A comparative study shows that the BDS chart detects process disturbances faster than the standard bivariate T
2 chart and the adaptive bivariate T
2 charts with variable sample size and/or variable sampling interval.
Acknowledgements
This work was supported by CAPES – High Level Staff Improvement Coordination –, CNPq – National Council for Scientific and Technological Development and FAPESP – The State of São Paulo Research Foundation. We would like to thank the new editor who handled the review process for this article.