Critical to Quality (CTQ)

Critical to Quality (CTQ) is a pivotal concept in the Lean Six Sigma methodology, serving as the keystone for achieving excellence in both product and process outcomes. CTQ is the most crucial and measurable characteristic of a product or process, directly linked to customer satisfaction. This metric acts as the bridge between customer requirements and the essential problem targeted for improvement within a project.

Determining CTQ

Identifying CTQ is the foundational step in the DMAIC (Define, Measure, Analyze, Improve, Control) approach. Typically, a project focuses on one or two CTQs. The CTQ must be expressed in an objective, measurable manner, although it does not always have to be numeric. Occasionally, the Voice of the Customer (VOC) closely aligns with the CTQ, eliminating the need for artificial distinctions.

Tree Diagram (CTQ-Flowdown)

In the Measure phase, the Tree Diagram, also known as CTQ-Flowdown, plays a crucial role. This diagram visually represents the hierarchy of factors contributing to the Voice of the Customer. The process involves placing the Voice of the Customer at the top level, with all contributing CTQs listed below. During this phase, the project team, including the customer/sponsor and project leader, selects the CTQ based on the highest need for improvement. Subsequently, the chosen CTQ may be translated into a clear and measurable Project-Y.

Quality Function Deployment (QFD)

Quality Function Deployment, commonly referred to as the House of Quality, is another valuable tool in CTQ analysis. QFD aids in ranking potential CTQs based on their contribution to the defined main Voices of the Customer. This method ensures a systematic approach to prioritizing CTQs, helping the project team focus on the aspects that have the greatest impact on customer needs.

Specifying CTQ

The final step involves specifying the CTQ by defining clear and measurable specifications. This ensures that the results are tangible and can be effectively measured against the established standards.

Examples of CTQ and Specified CTQ:


– Answer questions quickly
– Delivery before or on the delivery date
– Question addressed in a simple way

Specified CTQ:

– Answer questions in <45 minutes
– Delivery on the delivery date before 17:00
– Question answered after one phone call

Prioritizing CTQ

Given that the Voice of the Customer can often be translated into various CTQs, it is essential to prioritize them. To maintain project manageability, only one or two CTQs are typically addressed per project. Involving the customer or a customer panel in the prioritization process is preferable. Tools such as the tree diagram and QFD aid in determining which CTQs contribute most significantly to the targeted VOC.

In conclusion, mastering the concept of CTQ is fundamental for Lean Six Sigma projects, ensuring a focused and effective approach to meeting customer needs and enhancing overall organizational processes.


CTQ is covered during our Yellow Belt, Green Belt, Black Belt Services and Black Belt Manufacturing training courses.

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