選擇一個良好的供應商可以明顯地降低作業成本，增加市場佔有率。品質始終是企業選擇供應商最重要的指標。在各種品質管制與品質保證活動中，製程良率指標 與良率是一對一的關係，因此其提供了一個很精確的方法衡量製程表現。本文考慮觀察值為一因子隨機效應模式下，推導出 的估計量的近似抽樣分配，並進一步提供檢定良率方法。本研究可幫助品質工程師做較可靠的決策。

A right supplier can obviously reduce operation cost and increase the market share. Quality is always the key factor for selecting the better supplier. Among various quality assurance activities, index provides an accurate measure for process yield because the relationship between it and the process yield is one-to-one. In this study, we derive the sampling distribution of the estimator of based on the one way random effect model. The result can help the quality engineer to make more reliable decision.