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A well-written Critical to Quality (CTQ) characteristic becomes a goal for aligning the Lean Six Sigma project activities. A poorly written CTQ leads to confusion in the analysis and uncertainty with respect to the project's success or failure. There is a recommended template and format for writing CTQs.

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Quick reference

Writing CTQs

Writing a CTQ translates the Voice of the Customer into a specific Lean Six Sigma project goal.

When to use

CTQs are created and updated during the Define and Measure phases. As internal and external customer needs are identified, they must be translated into a written CTQ.

Instructions

Customer needs are often vague or at a level that is not actionable by a Lean Six Sigma team. Translating the customer needs into a written CTQ provides a measurable goal for the Lean Six Sigma team to achieve. A well-written CTQ will include four elements.

  • Product feature or process output characteristic that is associated with the customer's need
  • A measurable attribute of the characteristic – often the “Y” in the Y=f(x) equation.
  • A target for acceptable performance of the attribute.
  • Specification limits on the target that could be “greater than”, “less than”, or a tolerance around the target.

When developing CTQs, follow this process:

  1. Start with one of the product or process functions or features.
  2. Identify what the customer wants that function or feature to accomplish for them.
  3. Often the initial description of what the customer wants is vague or general, so ask the questions, “What does that mean”” to get a more specific understanding of the customer's need.
  4. Continue asking, “What does that mean?” until you have an actionable and measurable need.

Write the CTQ in the format: “The product/process function” performs “the customer need” in this “measurable manner.”

Hints & tips

  • CTQs should have a measurable component based on an objective standard (not a feeling).
  • In the Define phase, you will often have high-level CTQs.  In the Measure phase, those are often deployed down to specific product features or process steps and become much more specific.
  • An example of a well-written CTQ for internet access in a hotel room is; “The room provides a wireless internet signal to the desk/workspace area that is at least 4 bars strong.”
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  • 00:03 Hi, this is Ray Sheen.
  • 00:05 Writing CTQs is a skill that every Lean Six Sigma team member should acquire.
  • 00:11 Let's look at some of the best practices.
  • 00:14 I'll start by reviewing the importance of translating the voice of the customer
  • 00:18 into a CTQ.
  • 00:20 The customer does not know or care about the CTQ.
  • 00:24 They know what they want to happen with regard to the product or service.
  • 00:28 To get the voice of the customer, we need to understand what they want.
  • 00:32 Often you will get vague or high-level comments from them.
  • 00:36 Comments like, they want it fast, or they want it to be easy to use.
  • 00:39 These requirements, or as I often refer to them as desirements,
  • 00:43 must be translated into actionable goals for the project team.
  • 00:48 Just as a side note,
  • 00:49 some people refer to these as critical to customer when still in the customer terms,
  • 00:53 and they don't become critical to quality elements until they've been translated.
  • 00:58 There are four elements to a CTQ.
  • 01:00 It identifies the product or service features that are the focus of the CTQ.
  • 01:06 It includes a measurable attribute or characteristic of the product or
  • 01:10 service and defines an objective measurable achievement point to indicate
  • 01:15 when the CTQ is met.
  • 01:16 Finally, it includes if there is any tolerance or a less than or
  • 01:20 greater than criteria associated with meeting the target value of the CTQ.
  • 01:26 Let's look at the four elements of CTQ with some examples.
  • 01:31 The customer using the call center complains,
  • 01:33 I never get to the person I need.
  • 01:36 Well, the feature is that they need to talk with the correct person.
  • 01:39 The measurable attribute is pretty easy, that they talk to someone.
  • 01:43 The target value is that the connection is made with the correct person and
  • 01:47 a tolerance is zero misses.
  • 01:49 Let's consider another one.
  • 01:51 The customer tells us, we don't want any damage to these parts.
  • 01:55 The feature is shipping performance.
  • 01:57 The product is received without any shipping damage.
  • 02:01 The target is at the parts within spec and that includes any of the spec tolerances.
  • 02:06 One final example, the customer tells us,
  • 02:09 everything needs to fit together smoothly when assembling.
  • 02:14 The feature is a fit of parts and in particular,
  • 02:17 it is the dimensions at the interfaces.
  • 02:19 The target is the drawing dimensions for each part, and
  • 02:22 if there's no specified tolerances, we use our company standard policy,
  • 02:27 which in this case is plus or minus two thousandths.
  • 02:30 You may find that you need to take complex voice to customer comments or
  • 02:35 high level CTQs and
  • 02:37 flow them down into detailed level CTQs as you move forward in your project.
  • 02:42 By this time, you may be thinking,
  • 02:44 how is this any different from listing the customer requirements?
  • 02:49 Well, think of a CTQ as a unique method for
  • 02:51 how those requirements are identified and described.
  • 02:55 The team doesn't work from a sterile,
  • 02:57 multi-page requirements document that's full of jargon and boilerplate phrases.
  • 03:01 Instead, they're very specific and
  • 03:04 practical requirements right from the customer.
  • 03:07 Let's consider how to write one.
  • 03:10 Start by listing the major function or attribute of the product or
  • 03:14 process that the team is analyzing.
  • 03:17 For each of these functions,
  • 03:18 list specifically what the function must do from the customer perspective.
  • 03:23 That includes both internal and external customers.
  • 03:26 By that I mean, we don't describe how it works,
  • 03:29 rather we describe what the customer will do with the result when it works.
  • 03:34 A great technique that I use to help with this is when I list the function I start
  • 03:39 asking the question, what does that mean from the customer perspective?
  • 03:44 I continue asking that question several times until I have a measurable attribute.
  • 03:49 Then I'm ready to write it up.
  • 03:51 The format that I use for writing CTQ's is, the product or
  • 03:56 process function performs the customer need in this measurable manner.
  • 04:02 This tells me what is happening for what purpose and how to measure success.
  • 04:07 Let me walk you through an illustration to show how this works.
  • 04:11 This illustration is near and
  • 04:12 dear to me because I spent a lot of time in hotel rooms.
  • 04:15 I'm working at the client's facility during the day.
  • 04:18 And then at night, I'm in the hotel room preparing for the next day and
  • 04:22 doing whatever other business paperwork I have to for my business.
  • 04:26 So we start with the product function, in this case, the workspace in a hotel room.
  • 04:31 Next, there are the customer needs with respect to the workspace.
  • 04:35 I need a comfortable chair, a desk, several electrical outlets and
  • 04:39 a strong internet connection.
  • 04:41 Let's take that last one and turn it into a well-written CTQ.
  • 04:45 So I ask, what does a strong internet connection mean?
  • 04:48 And I get the answer,
  • 04:50 my laptop connects to an internet through its wireless system with a strong signal.
  • 04:55 That's helpful, but it's not yet measurable.
  • 04:59 So I ask the question again, but this time with more specificity.
  • 05:03 What does a strong signal mean?
  • 05:06 And now I get the answer, wireless signal strength at the desk area in each
  • 05:11 room has at least four bars out of five.
  • 05:14 Now that's better, that's something I can measure.
  • 05:16 I then can put everything into my CTQ format and I get,
  • 05:20 the room provides a wireless internet signal
  • 05:23 to the desk workspace area that is at least four bars strong.
  • 05:29 Well written CTQs will make it easier to define the problem and
  • 05:33 to focus the data collection.
  • 05:36 Ultimately, the project success will be measured based upon achieving the CTQs.

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