According to Smith, what is essential to control to achieve better quality?

Achieving better quality in processes and products hinges significantly on the control of variation. Variation refers to the differences that occur in a process or product, which can arise from numerous sources, including materials, machinery, methods, and human factors. By focusing on minimizing variation, organizations can produce more consistent and higher-quality outcomes.

When variation is controlled, it leads to improved predictability of processes, lower defect rates, and a higher level of customer satisfaction. In the context of Six Sigma, the strategy is fundamentally about reducing variation to ensure that processes operate within defined limits and consistently meet quality standards. This aligns with the overarching goal of Six Sigma to achieve near-perfect quality levels.

The other options may be important aspects of operational excellence but do not encompass the overarching principle of quality improvement as effectively as controlling variation does. Product variety can complicate operations and may introduce additional variation if not managed properly. Employee turnover can affect quality indirectly through the loss of knowledge and skills, while material costs, although important for financial aspects, do not directly address the consistency and reliability of the quality of products or services.