CTQ – Translating the voice of the customer
CTQ (“Critical to Quality”) translates vague, qualitative customer wishes into specific, measurable requirements. The CTQ tree leads from the need via quality drivers and performance requirements to the measurable characteristic (CTQ). Separately, the translation matrix defines the specification for each CTQ: measurement method, target value, limits and defect definition.
Context: Six Sigma · DMAIC – CTQ belongs in the define phase +
D · Define
- What is the problem?
- Who is the customer, what do they want? (CTQ)
M · Measure
- How big is the problem?
- How is it measured (Y)?
A · Analyze
- What causes the problem?
- Which variables act (X)?
I · Improve
- What solves the problem?
- Which X settings are needed?
C · Control
- How do you hold the solution?
- How do you secure improvements?
Translate the voice of the customer
From the vague verbatim quote via the core problem to the concrete, measurable requirement.
CTQ tree
Need → quality driver → performance requirements → CTQs (measurable characteristics with a unit). Each level branches 1:N – a requirement can have several CTQs. The limit values follow separately in section 3.
CTQ translation matrix · specification
Here – and only here – the limit values live. Per CTQ: measurement method, target value, specification limits and the defect definition that follows from them.
1Characteristic
What is measured?Waiting time until served [min]in the CTQ tree2Measurement method
How, with what, from when until when?Stopwatch: sitting down → order takenhere in the matrix3Target value
Where should the process aim on average?Target 3 minhere in the matrix4Limits
What do customers just still accept?USL 5 min · no LSLhere in the matrix5Defect
From when is it a defect – and how often is it permitted?Defect: over 5 min · at most 5%follows from 4CTQ ≠ limit value: the CTQ is the characteristic. Target and limits are its specification – they can change, the characteristic stays. LSL = lower, USL = upper specification limit. Leaving a field empty = one-sided specification.
Derive the limit from customer data
Helps with section 3: for a CTQ from the matrix, customer data shows from which value satisfaction drops. That is where the limit belongs – adoptable into the matrix with one click.
Guide: how to proceed
Choose a step.
Video companion · Questions & answers
All the terms from the video – in plain language. Click a question to open the answer.
What is CTQ? +
CTQ (“Critical to Quality”) is a method from strategic quality management used in the define phase of a Six Sigma project. Aim: to translate the voice of the customer – that is, vague, qualitative wishes – into specific, measurable performance requirements.
A good requirement …
- is specific and measurable,
- relates directly to an attribute of the product or service,
- does not prescribe a particular solution or technology (no bias),
- is complete and unambiguous,
- describes the what, not the how.
The CTQ tree
It gives an overview from the voice of the customer down to the detailed CTQs and consists of four sections: needs (critical customer needs), quality drivers (what fulfils the need), performance requirements (concrete requirements per driver) and CTQs (the measurable characteristic per requirement, with a unit).
Specification – separate from the characteristic
For each CTQ the specification is then defined: how it is measured (operational definition), which target value is aimed for and where the specification limits lie – one-sided (e.g. waiting time at most 5 minutes: USL only) or two-sided (e.g. room temperature between 19 and 24 °C: LSL and USL). From this follows what counts as a defect.
Remember: the CTQ is the characteristic (“waiting time until served”), the limit is its specification (“at most 5 minutes”). The short form “waiting time < 5 min” is fine as a mnemonic – in the working document the two are kept separate.
How saving works +
This HTML file is your document. Everything you enter ends up in exactly this file when you save – just like a Word document. If you pass the file on, all analyses in it go with it.
Save (green button or Ctrl+S) stores the current state – without any prompt. As long as no working file of your own has been created, the state is kept in the browser and is there again the next time you open it.
Save as (under “CTQ analyses”) creates a file on your hard drive. This is the only place where you are asked where to save. After that, every further Save writes silently into exactly that file.
The first time: open the file, click “CTQ analyses” and then Save as. From then on the green button is enough.
Saved automatically: as soon as an analysis has been saved once, the tool backs up every further change by itself after a few seconds.
If something goes wrong: the tool continuously keeps an interim state in the browser. If the browser crashes or you close the window by mistake, your work will be back the next time you open it.
Note on browsers: writing directly to the file currently works in Chrome and Edge. In Firefox and Safari everything stays saved in the browser – the file itself remains unchanged.