Welcome to the “House of Quality,” as the XY matrix is also called, another tool for use in the Measure phase. That’s because the XY matrix is used to link your customers’ critical-
to-quality (CTQ) require- ments to your process inputs, to ensure you have the right set of priorities in your process-improvement activities.
How? By taking a high- ly structured approach to brainstorming.
XY matrix A group of rows and columns, with one set of increments marked along the X (horizontal) axis and another set of increments marked along the Y (vertical) axis. Also known as an x-y matrix.
Brainstorming
Brainstorming is a method for generating ideas.
Participants focus on a problem or an opportunity and
come up with as many ideas as possible and push the ideas as far as possible.
During brainstorming, there is no criticism or discussion of any ideas; the point is to generate ideas and expand thinking about the problem or opportunity. As participants mention their ideas, some- body records the ideas on a board or a flipchart. (If the focus is on causes of a problem, the cause-and-effect diagram described below is useful for keeping track of ideas.) Participants can build on each other’s ideas.
Then, after brainstorming, the team can analyze the results and explore the best ideas. Brainstorming is also a valuable tool for prob- ing during the Analyze phase and for generating ideas during the Improve phase.
Cause-and-Effect Diagram
This graphical tool can be used to identify the relationship between a problem and possible causes of the problem.The structure resembles a simplified fish skeleton, hence another name for this tool, the fishbone diagram. (It’s also called the Ishikawa diagram, because it was popular- ized by Kaoru Ishikawa, a pioneer of quality management processes.)
The primary branch (spine) represents the effect and is typically labeled on the right side of the diagram, as the head of the fish. Each major bone branching out from the spine corresponds to a major cause or class of causes. Minor bones branching off from major bones correspond to more detailed causal factors.This type of diagram is useful in any analysis, as it illustrates the relationship between cause and effect rationally.
What I mean is that you and your project team can list the inputs for the particular process and then compare them with a list of outputs that are really important to your customers. The purpose for using the XY matrix is to study and understand the relationship between what you’re putting into a process and
what your customer is get- ting out of it. The XY matrix allows the team to identify gaps, areas for improvement.
So you develop a matrix that demonstrates thatY is a function of X:
you line up the process inputs (the X’s) against the process outputs (the Y’s that are functions of those inputs) (Figure 7-5).
Effect:
Shortage of Parts Measurements
Database not current Machines
Computers Bugs in scheduling softwar
e People
Staff shortage
Poor communication Training
Methods No communication
of back orders
No verification procedure Borrow from
other kits No r ecor
ds kept
Materials
Stock purge Lost parts
First-level subcauses Potential root
cause Second-level
subcause
Figure 7-4. An example of a cause-and-effect diagram showing causes for the effect, shortage of parts
Informed Opinion vs. Superficial
Emotion
At first glance, it may seem that the XY matrix is contradicting everything you’ve learned about Six Sigma so far, because it’s based on opinion, not fact.
But the important thing to remember here is that the opinions are informed:
the matrix is based on the team’s expertise and on thoughtful, construc- tive group analysis of the issues.
1 2 3 4 5 6 7 8 Ball hardness Ink viscosity Metal barrel Ball flow
Easy to hold Ink flows easily Does not smear Large ink capacity
4 1 2 3 Design Requirements Impor
tance Rankings Quality/
Customer Requirements
Strong Positive Correlation Positive Correlation
Negative Correlation Correlation Matrix Notation
Strong Negative Correlation Correlation
Matrix
Relationship Matrix Notation Strong Positive = 9 Medium = 6 Small = 3
Relationship Matrix
12 27 9 15
Importance Weighting
Figure 7-5. An XY matrix (house of quality) showing a simple exam- ple of a ballpoint pen and the connection between design and customer requirements
What’s a Good Cup of Coffee?
The hotel coffee service example presented in Chapter 2 illustrated how differently providers and customers can view
critical-to-quality (CTQ) factors.This is where the XY matrix can help.
First you list the output variables—in this case taste, aroma, price, and acidity—and then you rate them on the scale from one to 10. For example, taste and aroma would be a 10, but acidity would probably be only a two (or somewhat higher for customers with sensitive stomachs). So you’ve narrowed down key customer CTQ factors to taste and aroma.
Then, you rate your key input variables—which include coffee type, amount, grind level, water temperature, brew time, and cup type and size—against the output variables.This time, you can get at some solid information, such as the relationship between coffee type and taste and aroma. Since taste and aroma are huge CTQ factors, there’s a direct correlation between coffee type and taste and aroma, which gives your project team the information it needs to start fixing the process.
(There’s that simple formula again: Y = f(X). Output Y is a func- tion of Input X.)
Then the members of the team rate the inputs on a scale of one to 10 in terms of their importance to the customer. Next, you then rate the input variables against the output variables using the same scale, based on the relationship between X and Y. You end up with a blueprint of the input factors that most affect the outcome, what your customer wants.
With the XY matrix, you’re trying to prioritize what people think and believe about a given situation. Then, you can go and collect data that will validate those beliefs. Again, it’s not about guessing; it’s about disciplined thinking on customer priorities.
The XY matrix is a directional tool; it points out what you think are the suspect variables in a process so you can start measur- ing them.
As in process mapping, a manager’s role is to ensure the active involvement of team members, remove barriers, serve as a check-and-balance for the outcome, and be certain that the team’s consensus on key data actually represents the cus- tomers.