Critical To Quality Characteristics

An important term that we use in Lean Six Sigma is ‘critical to quality characteristic,’ or CTQ.  In order to understand what a CTQ is, and the role it plays in services, we have to start with the concept of deterministic reasoning.  As I described in a previous blog, deterministic reasoning states that our output (i.e. a service provided to a customer and the resulting service experience) is a direct result of the process we use to provide the service, and the inputs that go into it.  The critical to quality characteristics describe the output (the service and customer experience).

A CTQ is a measurable characteristic of the service that you provide to your customers.  It is something that must exist within the service in order for the customer to say that what you have delivered is good.  When it comes to quality, the customer is the ultimate judge of whether or not something is good.  They base their opinion on whether or not those factors they consider to be critical to quality exist, and the level of performance each factor exhibits.  As an organization, we also have a say in the CTQ's and their corresponding performance levels, but our standards have to equal or exceed those of our customers.

When I present critical to quality characteristics in a class, I like to use a bottle of drinking water as an example.  Let's say that you are going to buy some water to satisfy your thirst.  What would you look for in a bottle of water in order to say that it is ‘good,’ and that you would be willing to purchase it?  There are two key elements to consider – the water, and the bottle in which it comes.  Let's start by looking at the water.  If you're the customer, what characteristics will the water have to possess in order for you to say that it is good, and you would be willing to drink it?  Here are a few examples of characteristics that have been suggested as critical to quality when it comes to water:

  • It must be clean
  • It cannot have anything floating in it
  • It must be clear / colorless
  • There can be no chemicals present in it
  • There can be no viruses or germs in it
  • It cannot have a bad or stagnant smell
  • It cannot taste bad to the person drinking it
  • It must come from a source we are comfortable with (natural spring, a mountain stream, be specially filtered, etc.)

I am sure there are other critical to quality characteristics that could be added to this list, but I think that covers the key CTQ’s.  Now let’s look at the bottle the water comes in.  Examples of characteristics that have been suggested as critical to quality are that the bottle:

  • must not leak
  • must have a lid that can be sealed
  • must have an opening that is easy to drink from
  • must be recyclable
  • must be disposable, so a person does not have to carry it around all the time
  • must hold enough water to satisfy the drinker’s thirst
  • must fit in a cup holder
  • must be made of plastic that is thick enough to not break if dropped
  • must be easy to grip and feel good when held in the hand

As with the water, there are other critical to quality characteristics that could be used to describe the bottle but are not listed here.  There are also some additional factors that a customer could consider to be critical to quality when selecting water, but are not a part of either of the previous categories.  These include things like the brand or whether the water is provided at a temperature that is pleasing to the customer (hot, cold or room temperature).

I have had the opportunity to present the CTQ concept to students in sustainability classes here at Arizona State University.  Almost without fail, the students will focus on the fact that I am using a disposable plastic water bottle as an example.  I will be informed that water bottles of this sort are not environmentally friendly.  I have started taking these water bottles into the sustainability classes on purpose in order to start this line of discussion.  The lesson not only introduces the idea of critical to quality characteristics, but helps the students see that there is a need (a convenient and easily portable source of drinking water) that must be fulfilled in a way that eliminates the disposable bottle.

Similarly, we must look at what our customers need our services to provide, and then use that knowledge to find the best way to provide those services while delivering the critical to quality characteristics.

The water bottle is an example of a physical product that a customer would purchase.  Now let’s look at a service that we have all experienced – having a waiter or waitress wait on us in a restaurant.  The list of CTQ's for this type of service will vary from customer to customer; however, some common CTQ's that we might define for this service could be that we want:

  • the person waiting on us to show up quickly after we are seated
  • our waiter or waitress to be clean and presentable
  • the waiter or waitress to take our order accurately and ensure that we get the food we want, prepared the way we want it
  • our drinks kept filled and are refilled before they are empty
  • the waiter or waitress to walk by every few minutes to look and see if we might need anything
  • the waiter or waitress to periodically ask us if we need anything
  • someone to remove any empty or extraneous dishes from the table
  • the waiter or waitress to bring the bill and take our payment quickly when we are done

Some of the CTQ’s listed in the example above could be applied to almost any service.  Factors such as being attentive to customers, providing services quickly and accurately, and effective communication all play a role in service interactions.

As you examine the services you are providing to your internal and external customers, put yourself in their shoes and think about what they would consider critical to quality.  You will most likely come up with a pretty accurate list, and this will be a good starting point for assessing how well your services meet customer needs.  You will, however, need to confirm this by collecting input directly from your customers.  To do this, you need to go out and collect voice of customer (VoC) data from them.  Collecting VoC information will allow you to ask specific questions about your customers’ needs and what they define as being critical to quality.  You can reference my previous blogs, Hearing the Voice of Your Customer Parts 1-3 to learn more about gathering this type of information.  As always, I welcome your questions or comments.  You can email me at

About the Author:
Clayton Taylor, MBA, is a Management Research Analyst, Pr. and Certified Six Sigma Master Black Belt working in the Office of the Executive Vice President, Treasurer and Chief Financial Officer at Arizona State University. He currently consults with nine diverse Business and Finance operational areas to lower costs, improve operational efficiency and provide the highest quality customer experience to internal and external customers. Mr. Taylor can be reached at