Meaning
Quantitative ratios measure the proportion of nonconforming units within a specific production lot or over a set period. This calculated defect rate compares the number of failed pieces to the total volume produced or inspected. It focuses on the frequency of errors and does not measure the severity of individual failures.
Statistical Method
Quality departments calculate this figure using data from random samples taken during final inspection. When the defect rate exceeds the acceptable quality limit, the entire batch is rejected and held for sorting. This prevents the shipment of substandard goods to the distribution center.
Process Control
Control charts track these percentages over time to detect shifts in machine performance or material quality. A rising defect rate shows that the manufacturing process is drifting out of control and requires immediate adjustment. Operators must stop the line to find the root cause of the variation, which prevents the generation of scrap and keeps the yield within commercial targets.
Commercial Impact
Purchase contracts establish maximum allowed levels of nonconformity for every shipped batch. If the defect rate is higher than agreed, the buyer can demand a price discount or return the shipment. High average rates of nonconformity often lead to the supplier being removed from the approved vendor list.
