傳統上工業界係透過管制圖與直方圖對製程進行長期與短期製程能力分析，藉以了解關鍵品質特性的表現。當發現製程表現不佳時，便著手進行品質改善。而改善的成效除了藉由製程能力指標反映改善前後的結果外，工程師們亦應透過成本/損失的估算以凸顯品質問題的嚴重性，使高階主管能重視品質改善的迫切性而予以全力支持。因此透過損失成本的概念來探討多變量製程能力指標及其所對應之期望損失再進行製程改善，將更能反映製程改善的成效。
本研究係探討並建立產品品質特性呈望目及望小特性情形下，Taam et al. (1993)之多變量製程能力指標MCp和MCpm及Pan and Lee (2009) 所提出之新多變量製程能力指標NMCp和NMCpm，與多變量田口二次之期望損失間的關係式，以方便從事品管人員在進行對多變量製程期望損失估算時的參考。此外，我們將二變量常態分配下多變量製程能力指標MCp值及其所對應之不良率繪製成可供業界查詢之對照圖。最後，我們以兩個數值實例說明藉由多變量製程能力指標估算期望損失之流程與步驟。

Traditionally, engineers perform the long-term and short-term process capabilities to analyze the performance of key characteristics by using control charts and histograms. Quality improvement actions will be taken if the process is not capable of meeting specifications. In addition to use multivariate process capability indices to reflect the results of quality improvement, engineers should highlight the seriousness of the quality problem through cost /loss estimation, so the senior managers will pay more attention to the urgent need of quality improvement projects and render their support. In the research, we show that the expected quality losses can be estimated by the given multivariate process capability indices. The relationship between various formulae of multivariate process capability indices and Taguchi’s quadratic losses that been established for the nominal-the-better and the smaller-the- better case. Then, the correspondence figure between various MCp indices and then nonconforming rates are provided.
Finally, two numerical examples are given to demonstrate how the expected losses can be estimated by the given multivariate process capability indices. Hopefully, the research results are useful for quality practitioners in estimating the quality losses for multivariate manufacturing process.

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