Defining the voice of the customer
In a previous post I talked about the Kano model as a tool to help define customer value. There are many more, like critical to quality tree, usability map, empathy map, ethnographical research, focus groups and customer journey maps. Over time we will get to them all. Today it is time to look at one of the fore components of six sigma: The critical to quality tree or flowdown chart.
Why use a critical to quality tree?
A critical to quality tree helps you to define broad and qualitative customer demands into specific, actionable and measurable performance requirements. These performance requirements can be used to measure how your value stream succeeds in delivering the desired value to the customer. The customer can be external, but also internal. When you make a critical to quality tree for internal purpose you ensure that transfer from one process to the next will work as smoothly as possible.
How do you make a critical to quality tree? (CTQ tree)
1. Describe your products and it’s expected customers
It is important to make these descriptions explicit. At times we get the purpose and target audience wrong, making our assumptions explicit helps in identifying mismatches between expectations and reality. When it is an existing product this does not have to take very much time, when it is a new product it may take a bit longer. When you notice in discussing this that people cannot agree, you can choose to test both viewpoints during later phases of defining your CTQ tree. Try to keep this phase as data driven as possible. Be aware of data that may not be available and how that may affect your assumptions.
2. Identify critical needs
You need to ask your customers about what is critical for them about this product or service. It works best when you define these critical needs in broad terms. You can make a critical to quality tree for each critical need.
When you ask customers be sure to use both an etic and an emic perspective. You can use focus groups, interviews, surveys, fieldwork and so much more. When you talk to customers be sure to ask both detractors and promoters of your product and brand. This will yield the most valuable insights.
When you cannot ask the customer use creative methods to get at the critical needs. You can use the six thinking hats and braimstorm methods. When you do this, be sure to include front line staff who interact with customers on a daily basis. Here as well mixing up the group with early adopters and critical people will help in increasing quality.
Most critical needs come from these perspectives:
- Quality (meets specifications)
- Speed (cycle times, lead times, timeliness)
- Safety (number of mishaps for each x)
- Reliability (number of defects for each x)
- Flexibility (number of change overs for each x)
- Costs (money and time)
3. Identify quality drivers
You need to identify all quality drivers for each critical need. It helps to take time for this phase. When you rush this, you may overlook important information. When you miss quality drivers your CTQ tree will yield a mismatch between customer expectation and your own metrics.
You can use the same methods as mentioned in step 1 and you can plot the drivers on the Kano model.
4. Identify performance requirements
You need to identify the minimum requirements for each quality driver. There will usually be more than one requirement for each driver. Your performance requirements need to be measurable. This can be on a scale, but it can also be Boolean (true/not true) in nature. Since you start with broad critical needs you may well needs several levels or performance requirements to get to a level where you can measure them.
5. Implement the measurements and tools needed to fulfill the performance requirements
Once you have a complete critical to quality tree, you need to make performing to its requirements a reality. Being able to perform at a consistently high level depends on many factors: training and skills of people, machine performance and availability, suppliers, tools and delivery to name just a few. There are many ways to go about this, but some of the key tools tend to be the same even if the results may look very different for each company. These are the tools most often used to make the CTQ tree a reality: