The fishbone diagram, cause and effect, or ishikawa diagram is one of the most common quality tools used today. Best known by its resemblance to a fish's body the fishbone diagram is used to show the many possible causes for an effect. The tool is used to help coordinating brainstorming in an effort to discover root causes.
In almost every project you perform in both lean and six sigma teams will bring a long list of experience, talent and solutions to the project table. But often times it can feel overwhelming when trying to decide which of the solutions to move forward on, especially if you have limited time for implementation. So how do we complete this important project task without losing all of our hair?
What is the tool used for?
The cause and effect matrix, C&E matrix or XY diagram is a great tool that can do the job quite effectively. The XY matrix takes a list of possible X's and narrows them down into a more manageable amount of inputs. Similar to the way a PPI measurement works in selecting projects the C&E/XY matrix helps us to prioritize solutions for implementation.
How do we use the tool?
First and foremost let's recall our formula that we use in six sigma projects, Y=F(X). We will use this same formula in our C&E/XY matrix. The Y's or the red cells represent process outputs and the cells above our Y's which are yellow represent our customer's voice or the level of importance the outputs are to the customer. Next we have the grey cells which shows us our input variables or our X's. The X's are what input variables you will use in your attempt to accomplish the Y or customer desire. Finally we have our blue cells which tell us the level of impact or correlation each input has on the output. So let's define a process for using the C&E and walk through an example.
1. The first thing we want to do is define the the process outputs. This is simply the end result or customer desire that we are trying to achieve. Let's say we are listing some important outputs for a hamburger we are making.
will score each of the outputs on a scale of 10 to 1. 10 being the most important and 1 being the least important. For best practice your most important Y will be your only 10, however your other Y's can and may score the same.
Inputs could be anything from initiatives to projects or other activities you will use in order to achieve the outputs. There are many different ways that you can gather suggestions for improvements like brainstorming and gemba walking. Any way is acceptable just be sure to place those inputs in the grey boxes.
5. When this data is in the cells you see a total number and percentage number automatically populate. We first want to look at the total column. In the case of our hamburgers our priority would be first creating a standard for making the burgers, then adding a special sauce to our burgers. The way we read is by looking for the highest number and placing our options in descending order going down.
Although our hamburger example was only in theory the XY/C&E matrix will be a very valuable tool for your team to use when you have multiple solutions in mind. As always using any data that may exist is the best way to get the most accurate results, however if there is no type of data qualitative information will be very helpful. Just remember that if you use the matrix based on qualitative data that the best thing you can do to get accurate results is make the team cross-functional.