Establishing the initial list of potential causes is often more art than science.  Unfortunately, the brainstorming process is still one of the best ways to surface candidate variables.  However, there are several other alternatives:

1)   Query process experts.
2)   Benchmark similar processes.
3)   Review the literature.
4)   Perform an Internet search.
5)   Conduct correlation study.
6)   Observe the process.
7)   Analyze physical models.
8)   Conduct FMEA.
9)   Execute Fault Tree Analysis.
10) Develop C&E matrix.

Another effective approach involves the conduct of a simple “force field” analysis.  Such a procedure is also called a “T bar exercise.”  To execute this procedure, the “driving and restraining” forces are displayed as horizontal “force arrows” that are perpendicularly aligned along the vertical portion of the T-bar – much like straight pins sticking out the sides of a pencil, but where the pencil shaft has been vertically oriented on the table’s surface.

The intersect between the vertical and horizontal bars constitutes the “point of system stability.”  It is that point where the sum of all forces is zero.  Now we might ask: “How could this system be imbalanced?”  What factors would have to change in order to destabilize the steady state condition?

Many times, we might be able to think of a driving (or restraining) force that can be added (or deleted and then supplemented) to accomplish this task.  In other words, we say to ourselves: “What kind of counter force can be applied to upset the system?” In turn, this stimulates other thinking – thereby arousing an insight into to the identification of a variable (force) not previously considered.