目前已有許多有關生產經濟性（economics of production）和製程品質（process quality）之間互相影響的研究，但大多數的研究卻是將品質以非常傳統的觀點來看待，亦即「產品的品質特性（Quality Characteristic）是否超過設計所要求的規格界限來作為判定的標準」的二分法，但是這樣的結果不外乎只有允收與拒收的兩種情況。並不符合近代對品質強烈要求的趨勢，更可能低估了品質之重要性。所以本研究將品質的損失以田口對品質的觀點納入EPQ模式中考慮，為了使模式更一般化且具實用性，其中損失函數是以Li & Maghsoodloo（2000）所建立之二次截斷式損失函數為基礎，並假設超出上下規格界限之損失不同，同時考慮廢棄成本（reject cost）和重製成本（rework cost），以期更符合實際生產狀況，經由研究發現低估品質成本（亦即忽略田口損失）最後將導致更高的總生產成本。

另外研究中亦利用投資以降低製程的變異，並採用Hong & Hayya（1993）所提出之製程變異－投資函數，一併納入總生產成本模式中考量，除了得到變異降低與提昇製程能力的效果之外，管理者更可以利用本模式來比較不同製程改善模式之成本差異，提供管理者對製程改善模式選擇之決策參考，同時本研究所導出之最佳批量與投資解，可以提供管理者在生產決策的參考依據。

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