Return on investment (ROI) is a financial ratio that measures the profitability of an investment relative to its cost. ROI is calculated by dividing the net income (or profit) generated by the investment by the total cost of the investment. ROI is decreased by any activity that reduces the net income or increases the cost of the investment. Increasing cost of sales is an activity that decreases ROI because it reduces the net income generated by the sales revenue. Cost of sales (or cost of goods sold) is the direct cost of producing or purchasing the goods or services sold by an organization. Cost of sales includes materials, labor, and overhead costs. Increasing cost of sales means that the organization spends more money to produce or acquire the same amount of goods or services, which lowers its profit margin and ROI.

References: CPIM Exam Content Manual Version 7.0, Domain 8: Manage Quality, Continuous Improvement, and Technology, Section 8.1: Develop Quality and Continuous Improvement Plans, Subsection 8.1.2: Describe how to develop a business case for quality and continuous improvement initiatives (page 74).