The Six Sigma methodology uses facts and data to search for the root cause of problems that dissatisfy customers.  An important issue that we must come to grips with is how to take customer requirements and turn them into characteristics that we can measure to see how well we are meeting the requirements.  We need to define what are known as Critical to Quality Characteristics (CTQ’s) based on the Voice of the Customer.   Customers know what they want in general terms, but are often not capable of expressing those wants and needs in a concrete and objective way.
I included an exercise in our Green Belt course that challenges students to list several customer requirements, and then explain how they will measure how well a process is doing at satisfying the requirements.  Students often have difficulty expressing customer requirements as CTQ’s in objective, measurable terms.
Here are some examples of the translation that needs to be made in order to operate in the realm of facts and data using Six Sigma:
Customer requirement – a car with good fuel mileage.
CTQ – a specific number of miles per gallon, such as 35 miles per gallon.
Customer requirement – a fast internet connection.
CTQ – a specific number of megabits per second (Mbps), such as 100 Mbps.
Customer requirement – a firm mattress.
CTQ – a specific indentation load deflection (ILD), such as 40.  ILD is measured on a scale of 12 to 50, where 12 is the softest available and 50 is the firmest.  The higher the ILD number, the firmer the mattress.
Customer requirement – a strong cell phone signal.
CTQ – a specific Received Signal Strength Indication (RSSI) in decibels (dB), such as -70 dB.  The number of decibels will be negative, and the closer to zero the RSSI the stronger the signal.  For example, an RSSI of -80 dB is stronger than an RSSI of -90 dB.
Customers speak in terms of requirements, but processes are measured in terms of CTQ’s.  As Six Sigma practitioners, we must learn to be bilingual and speak both languages (customer and process).  If we are not able to do so, we will never be able to measure the current performance of the process, nor will we be able to know if we are meeting the requirements of the customer.
Your comments or questions about this article are welcome, as are suggestions for future articles.  Feel free to contact me by email at
About the author:  Mr. Roger C. Ellis is an industrial engineer by training and profession.  He is a Six Sigma Master Black Belt with over 45 years of business experience in a wide range of fields.  Mr. Ellis develops and instructs Six Sigma professional certification courses for Key Performance LLC.   For a more detailed biography, please refer to