The Defect Rate Trending Up Undetected

LINE-A's rolling 4-week defect rate has climbed steadily for 12 weeks, from 2.0% to 9.0% — a real emerging quality problem. But the weekly QA report only ever compares this year to the same week last year, and last year had its own one-off supplier defect spike in those same weeks (up to 8.0%), so year-over-year this week reads as "+1 point, not alarming." Four other lines are flat at 2% all year on both the rolling and YoY view.