CTQ Linkage


The CTQ linkage is a graphical depiction showing a clear link to the needs that are Critical to Quality (CTQ) from the perception of the customer. The chart begins with the most elementary needs and more levels are added as needed and exact metrics are not necessary at this time.

The CTQ breaks down customer requirements into quantified requirements. This may include targets and lower and upper specification limits (LSL and USL).

The customer is also the company you are representing and consideration to their requirements (ROI, cash, time schedule) is also important. Below is a very basic form of a CTQ Flowdown. 

Basic CTQ Flowdown


Solidify the connection between the targeted metrics to achieve customer satisfaction by mapping them to the Voice of the Customer (VOC).

The customer can also be the business itself, machine operators, and other stakeholders related to the business, not just the end users that are usually the thought of "customers".

All of the inputs impact the process. The inputs of the process create an output, "Y". The goal is to have "Y" linked to the needs and expectations of the customer. Customer needs are in the areas of cost, delivery quality, service, and more. The Voice of the Process (VOP) is described by the Process Output Variables (POV). The VOP is a function of all the inputs:

CTQ Linkage

The causes are the x's (or inputs). These inputs create a process output which the project strives to improve toward a target and reduced variation. These improvements must be directly linked to the critical needs of the customer.

These needs are labeled as the those being Critical to Quality, however, this pertains to any type of customer need and specification.

FOCUS ON the customer must-haves and needs before trying to implement delighter and surprise features or spending excess resources and money to achieve unnecessary levels of performance.

Y = f(x)

The Strategy behind Six Sigma

A customer may have high occurrence rate of defects that involve a part being too long and out of specification. The customer specifies a maximum length of 125mm +/- 5mm (this is the Voice of the Customer stating the LSL is 120mm and the USL is 130mm)

The output "Y" is the length. 

The Six Sigma team is dedicated to finding the inputs that affect the length of the part. The inputs are the x's. 

The length of the part "Y" is a function of several inputs or x's. 

  • Part Length = function of (x1,x2,x3,....xn)

Some examples of factors that affect the length could be the machine, methods, measurement system, material, and manpower and a further drill down into those areas will get deeper into the sources.

The strategy is to find the most critical inputs and determine the root causes to control so that the process creates the length as close to the target every time; but most of all with minimal variation from part to part. Once it is accurate and precise, put controls in the process so it is repeatable and reproducible. 

All this must be accomplished by team while maintaining the other metrics that are Critical to Quality or to satisfy the Voice of the Customer (such as on-time delivery and price). 

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