Module 2 · Lesson 9 of 16
CTQ and requirement trees
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Learning objectives
- Construct a requirement tree from need to metric.
- Maintain logical linkage between branches.
- Keep solutions out of the tree.
Need → driver → CTQ
Begin with the need, branch to requirement drivers, then to measurable characteristics. Branches should collectively explain the need without unnecessary duplication.
Garment-factory example
"Durable seam" branches into seam strength, slippage, stitch security, appearance after laundering and defined test conditions.
Method
- State the need at the root.
- Ask "what does this require?" repeatedly.
- Define measures at each leaf.
- Trace every CTQ back to its VOC source.
Common mistakes
- Adding "buy new machine" as a requirement.
- Using overlapping branches.
Knowledge check
Pick one answer per question. Explanations appear after you submit.
1. A requirement tree explains:
2. Which is a valid branch of "durable seam"?
Author: NOSK.life · Last reviewed: 2026-07-21