6 Sigma Series: Diagramming for definition in Six Sigma

To identify all the X’s (inputs) in our process that impact the Y’s (the critical output(s)) through brainstorming alone can be an impossible task. So, we try to add some structured documentation to the mix so that we can start to identify those X’s in a structured manner.

The first technique we can use is Affinity diagramming. This is a technique in which we work as part of a cross functional team; everyone in the team writes down their ideas on sticky notes & sticks them to the wall. After that, a short discussion around each idea will lead to categorization of identified X’s and enable us to start identifying those X’s with the most impact on Y.

Next, we can look at Fishbone diagrams. These are really useful as it enables us to bundle all of our identified issues into pre-defined categories, which helps to focus the team’s mind. These categories are fluid, that is to say, you’re not obliged to use a set list of categories, you can make your own that fit your organization. For example:

  • People, Place, Price, Promotion and Processes
  • Man, Machine, Method, Measurement, Environment, Material, Management, Maintenance

Once you’ve decided on the categories that work for your organization, we can start to map them onto a fishbone diagram. We start by placing the Y (output) as the head of the fish and we use bones coming from a central spine for each category. Along each bone, we then create smaller bones on which we write the team ideas.


Quantify and prioritise process risk

FMEA (Failure Mode Effects Analysis) helps us to quantify, prioritise and mitigate risk in a process. By doing this, we can focus in on the critical few factors that have the greatest impact on Y.

To do this, we create a table that holds each identified process step along with all of the below information.


Content based on study of the Six Sigma Black Belt course and Six Sigma for Dummies

Kieran Keene

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