品質不良コスト（COPQ）

Cost of poor quality, or COPQ, turns quality problems into a decision metric. It includes internal failure, external failure, rework, customer remediation, and estimated opportunity loss so teams can prioritize process improvement and service design with economic evidence.

COPQ = internal failure cost + external failure cost + rework + returns/warranty/credits + quality-driven opportunity loss. Formula | COPQ = internal failure cost + external failure cost + rework + returns/warranty/credits + quality-driven opportunity loss. | Use it as the primary operating calculation Bridge | Beginning COPQ + defect increase - prevention impact - detection improvement +/- demand and mix change = revised COPQ | Use it to explain changes between reviews Segment | Split by customer, product, channel, and period | Use it to find deterioration hidden by averages

This metric is comparable only when inclusion and exclusion rules stay stable. Include | Scrap, rework, returns, warranty, credits, complaint handling, quality-driven lost sales | They reflect economic impact Exclude | Normal prevention, inspection investment, necessary redundancy, training | These are investments in quality, not failure cost Define explicitly | Brand damage, churn, reputation risk | Estimation rules must be stable

Breaking the metric into drivers clarifies what action should follow the review. Defect rate | More defects increase scrap and rework Detection timing | Customer-discovered failures cost more than internal catches Process variation | Weak standardization increases repeat work

Use Cost of Poor Quality to decide prioritizing quality investments because it highlights defect rate and the inspection cost versus failure cost tradeoff. It changes prioritization by forcing teams to state the horizon, boundary conditions, and controllable drivers. It informs adjustments when rework time or customer impact shift, so decisions stay grounded in current conditions.

• Use Cost of Poor Quality to decide prioritizing quality investments because it highlights defect rate and the inspection cost versus failure cost tradeoff.
• It changes prioritization by forcing teams to state the horizon, boundary conditions, and controllable drivers.
• It informs adjustments when rework time or customer impact shift, so decisions stay grounded in current conditions.

• Define the unit and horizon before comparing defect rate across options.
• Keep the primary driver separate from secondary noise and one-off shocks.
• Document data sources, estimation steps, and confidence ranges for review.
• Translate the tradeoff into thresholds that can be monitored over time.
• Revisit assumptions when the market boundary or policy setting changes.

Do not decide from the number alone; align assumptions, period, segments, and companion metrics. Tracking only easy returns understates lost sales and reputation risk. More inspection alone can delay prevention work. Using COPQ for blame reduces reporting quality.

• Tracking only easy returns understates lost sales and reputation risk.
• More inspection alone can delay prevention work.
• Using COPQ for blame reduces reporting quality.

Companion metrics turn a good-or-bad reading into a discussion of causes and actions. Operational Efficiency | Waste and rework | COPQ reduction improves efficiency Process Improvement | Root-cause removal | Shows where to intervene Service Quality Calibration | Expected service level | Reduces external failure

A service team sees 20 returns, 80 hours of rework, and $3,000 in credits each month. Root-cause review shows most failures start in onboarding setup. Adding an automated check cuts rework in half, which makes the quality investment visible in financial terms. After the review, the owner did not treat the metric in isolation. They compared it with companion metrics, checked segment differences, documented assumption changes, and verified data quality before changing the plan. Whether the number improved or deteriorated, the team identified the driver, assigned an owner, and fed the learning into the next budget, operating review, or experiment cycle.

Quality management cost | Prevention and appraisal investment | COPQ is failure loss Customer support cost | Service effort | COPQ isolates quality-driven support Revenue loss | Churn or lost sales | COPQ counts the quality-caused portion

• Cost of Poor Quality is not a universal rule; results depend on boundary assumptions and data quality.
• A single metric like defect rate is not sufficient without considering rework time and customer impact.
• Short term movements can mislead when responses happen with lags.