Critical to Quality (CTQ) Trees
A CTQ tree breaks a vague customer requirement down into the specific, measurable characteristics a product or process must hit to satisfy it.
Specific numbers to hit sit at the base, rolling up through drivers to one customer need at the top.
Reach for this when…
- Customers say the product should be reliable or fast and nobody can turn that into a spec.
- You're running a Six Sigma or quality project and need a defensible link from need to metric.
- Engineering and customer service disagree about what quality actually means for this product.
How to run it
- State the customer need in the customer's own words.
- Break it into the drivers behind that need: what makes it true or false for them.
- Break each driver into a specific, measurable requirement.
- Set a target and tolerance for each measurable requirement.
- Check the tree back against the original need to confirm nothing was lost.
A worked example
Situation. Isabela Souza ran quality at Nordeste Auto Peças, an auto parts manufacturer in Recife, Brazil, where customers kept saying a brake component should feel solid, with no spec attached to the word.
Applied. She built a CTQ tree from solid down through the drivers, resistance to flex, consistent torque on installation, to measurable targets: flex under a specified load, torque within a set newton-metre range.
Result. The line started measuring flex and torque directly on every batch, and warranty claims tied to that complaint fell by half within two quarters.
The catch
A CTQ tree is only as good as the translation from customer language to measurable driver, and that step is where teams guess instead of asking. It also tends to freeze at launch and never get revisited as customer expectations shift. Rebuild it when the complaint pattern changes, not just once.
If nobody can trace a spec on the factory floor back to a customer's actual words, the tree was decoration.