Voice of the Customer (VOC) captures what customers need, expect, value or complain about. A Critical-to-Quality (CTQ) requirement converts that voice into a measurable characteristic the process can control. The key skill is moving from vague customer language to an operational definition.
VOC vs CTQ
| VOC statement | Possible CTQ |
|---|---|
| “Deliver on time.” | ≥98% orders delivered by confirmed date |
| “No damaged cartons.” | Damage rate <0.2% |
| “Orders must be accurate.” | ≥99.8% line-item accuracy |
| “I need quick responses.” | Customer query acknowledged within 4 business hours |
How to Build CTQs from VOC
- Collect customer input. Interviews, complaints, surveys, order history, service calls and account reviews.
- Group recurring needs. Separate quality, delivery, cost, service and compliance themes.
- Clarify what success means. Replace terms such as “fast,” “good” or “reliable” with observable outcomes.
- Define the measure. Specify the KPI, unit, target, tolerance and data source.
- Link the CTQ to process drivers. Identify which process inputs and controls influence the result.
- Validate with customers/users. Make sure the measure actually reflects what matters to them.
CTQ Tree Example
Need: “Reliable delivery.” → Drivers: correct quantity, confirmed date, undamaged product. → CTQs: OTIF ≥98%, damage rate <0.2%, order accuracy ≥99.8%.
Common Mistakes
- Treating a slogan such as “excellent service” as a CTQ.
- Choosing an internal KPI the customer does not value.
- Setting targets without a clear data definition.
- Using averages that hide critical failures.
- Failing to distinguish customer requirements from internal process controls.
VOC is commonly used in improvement methods such as DMAIC. For customer-priority analysis, see Kano Model.
Interview Question
Question: A customer says “I need faster delivery.” What do you do next?
Answer: Clarify the need and convert it into a measurable CTQ—for example, 95% of orders delivered within two days or OTIF above a defined target—then identify the process factors that drive that result.
Reference
American Society for Quality (ASQ) — Voice of the Customer and DMAIC resources.
Download the Practical Workbook
Use the SCMANA VOC to CTQ Template to convert customer statements into measurable requirements with clear KPIs, targets, tolerances, data sources and process drivers.
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