<h1 style="font-family:Verdana, Arial, Helvetica, sans-serif; font-size:x-large; color:#009933">CTQs in Six Sigma</h1>

Defining CTQs in Six Sigma:

After starting a project and gathering the voice of the customer (VOC), it is time to define the critical-to-quality outputs (CTQs).

CTQs are the key measurable characteristics of a product or process whose performance standards or specification limits must be met in order to satisfy the customer.

These outputs represent the product or service characteristics defined by the customer (internal or external). They may include the upper and lower specification limits or any other factors related to the product or service. Typically, a CTQ must be interpreted from a qualitative customer statement to an actionable, quantitative business specification.

Establishing CTQs is vital for a company to meet customer needs and keep up with the competition.

VOC Becomes CTQs:

The flowchart in Figure 1 provides an overview of the requirements necessary to translate the VOC into usable CTQs.

  

Operational definitions of the flowchart steps are:

·    Characteristics of product or service: A word or phrase that describes some aspect of the product or service. For example: T.A.T. (Turn Around Time to dry-clean a garment).
 

·    Measures and operational definitions: A definition of how the product’s characteristic will be quantified. There may be several ways of quantifying a given characteristic. For example: the unit used to measure time between when the cleaner receives clothes and when the clothes are ready for pickup (measured in hours).

·    Target value(s): The aim for a product or service, assuming that  there is no variation in the product - this is the value that is the desired level of performance. For example:  clothes ready for pickup in 24 hours.

·    Specification limits: How much variation is the customer willing to tolerate in the delivery of the product or service? Specification limits are performance limits that are acceptable to the customer. For example: Upper specification limit for dry cleaning process time maybe  28 hours.

·    Defect rate(s): This is how often the producer is willing to produce a product outside the specification limits. For example 3.4 defects per million opportunities for error.

Figure 1: Flowchart for VOC to CTQ

CTQ Tree:

CTQ tree is actually the abbreviated form for Critical to Quality tree. The CTQ tree indicates key measurable aspects of that process or product whose specification limits or performance standards must be met to fully satisfy the customer. It aligns developments or helps in designing efforts to adapt to customer requirements. More specifically, it is mainly applicable for decomposing broad customer requirements and change them into more easily quantifiable requirements. The CTQ Tree is often used in Six Sigma methodology.

The steps for creating and using a Critical to Quality Tree (CTQ Tree) are as follows:

Step 1

Identification of the key customer requirements - The team identifies the key requirements that the customers have for the product or service. This is done through a process of open discussion / brain storming.

Step 2

Identification of customer's first level of requirements - The team gets to identify two to three requirements which are able to resolve major customer needs as pointed out Step 1. Good customer service refers to the phones which are answered quickly by staff who are knowledgeable about the product.

Step 3

Identification of customer's second level of requirements – In this step, the team gets to identify two to three needs which further resolve each customer requirement as pointed out in Step 2. The phones which are answered quicker may be defined as being answered within 2 rings. Then a knowledgeable staff member may be able to answer 90% calls before transferring them to another individual.


Step 4

Stop after quantifiable requirements are reached - This step applies to a situation when the team reaches a level of requirement which can be measured. The team would then halt the process of identifying needs if these requirements become distinctly measurable.

 

Step 5

Confirm the final requirements with customers – This is actually the final step taken which is applied after all customer requirements over a CTQ Tree have been pointed out and identified to a certain quantifiable degree. Each of these requirements should actually be confirmed again with customers.

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