One of the tools used by many quality assurance functions is the cause-and-effect diagram.

Identify a problem (effect) with a list of potential causes. This may result from a brainstorming session.

Write the effect at the right side of the paper.

Identify major causes of the problem, which become “big branches”. Six categories of causes are often used: Measurement, Methods, Materials, Machines, People, and Environment, but the categories vary with the effect selected.

Fill in the “small branches” with sub-causes of each major cause until the lowest level sub-cause is identified.

Review the completed cause-and-effect diagram with the work process to verify that these causes (factors) do affect the problem being resolved.

Work on the most important causes first. Teams may opt to use the nominal group technique or Pareto analysis to reach consensus.

Verify the root causes by collecting appropriate data (sampling) to validate a relationship to the problem.

Continue this process to identify all validated causes, and, ultimately the root cause.