A source of variation is the component of a process that is responsible for some process variation. A cause of variation is a source of variation along with a reason or mechanism for the variation. Often identifying causes of variation in a process is of critical importance. So that input is obtained from as many different perspectives as possible, and so that critical factors not be overlooked, it is essential that the identification of causes of variation be a team effort, involving everyone with knowledge of the process.
An excellent way for the team to obtain a list of possible causes of variation is through brainstorming. In order to be successful in an organizational setting, a brainstorming session will bring different people, departments, groups, etc., together. It will use devices such as flowcharts and Ishikawa diagrams (which you will learn about shortly) to document and encourage ideas on causes of variation in the process. In order for brainstorming to succeed, all participants must abide by the cardinal rule of brainstorming:
ABSOLUTELY NO CRITICISM
The idea of brainstorming is to get as many ideas as possible from the team, not to show how brilliant you are. Though this often results in many outlandish ideas being put forth, there are two things to remember: first, many revolutionary ideas at first sounded outlandish (how do you think relativity theory sounded at first?); second, even an outlandish idea by one member of the team may inspire others to come up with valuable ideas.
Brainstorming should result in a large number of factors that might be causes of variation. Using data, knowledge and experience, the team should try to reach consensus on what are the major causes of variation. Only by understanding these causes of variation can the process be truly understood and improved.