The list derived from the detailed process map needs to be shortlisted. This can be done in multiple ways. The different tools that are commonly used in six sigma projects to meet the purpose have been written down. They are as follows:
Cause Effect Matrix: The cause and effect matrix takes the list of inputs from the detailed process map and then gives them an individual score based on the effect that they have on the various critical to quality parameters.
The rows in the cause and effect matrix are used to list down the inputs and the columns are used to list down the critical to quality output. The intersection cell between a row and a column is meant to carry the impact of the input on that specific output. The impact is rated between 1 and 5, 5 being the highest.
Finally, there is a total column, whereby the total impact of the input on various outputs is judged by multiplying the numbers. The inputs are then arranged in descending order and prioritised for action.
Priority Matrix: The priority matrix is a very important tool that can be used to successfully narrow down to a limited number of causes once you have a list of a large number of causes in place. The way to do so is a simple 2 by 2 matrix.
On one of the axis is the dimension of control. It has two classifications high control and low control. High control implies that the performance of the variables is within the scope of the project identified and can be completely controlled by the team involved. Whereas low control means that the performance of the variables may be beyond the scope of the project.
On the second axis is mapped the dimension of impact. Variables are classified as having high or low impact on the business opportunities that are in question.
The end result is that there are four categories of variables with their usual control plans like:
High Control and High Impact: The focus of the team.
Low Control and High Impact: Visit the champion as many variables may be out of scope.
Low Control and Low Impact: Ignore.
High Control and Low Impact: Consider cumulative impact of these variables.
Cause Effect Diagram: Also known as the fishbone diagram or the Ishikawa diagram, the cause and effect diagram is perhaps the most popular way of zeroing down on important inputs. It has been explained in detail in the later pages of this tutorial.
Failure Mode and Effect Analysis: Failure mode and effect analysis judges the possibility that a variable may be able to impact the project in a negative way. A FMEA score is arrived at which signifies the risk associated with the variable.
Six Sigma project leaders will often use multiple analysis. This helps them look at variables in different ways from different perspectives and also gives them assurance that they have zeroed down on the correct variables.