When to Use Cause And Effect Diagrams

To brainstorm potential underlying process factors that can be investigated, such as in a designed experiment; To generate a list of potential failure modes that should be addressed in the proposed solution

Cause And Effect Chart Methodology

Begin by brainstorming the potential relationships between the process and the outcome. The outcome, or effect, typically is stated in terms of a problem rather than a desired condition, which tends to help the brainstorming.

The major branches of the fishbone are chosen to assist in brainstorming or to categorize the potential problems afterwards. You may find it convenient to use either the 5M and E (manpower, machines, methods, material, measurement, and environment) or the 4P (policy, procedures, plant, and people) to either categorize on the final fishbone or ensure that all areas are considered during brainstorming. Categorizing the potential causes (as branches off the spine) can be helpful in the data collection or analysis. Sub-causes (or branches) are added as needed, and it is often helpful to go down several levels of sub-causes.

Bear in mind that the causes listed are potential causes because there are no data at this point to support whether any of the causes really contribute to the problem. In this regard, as in all brainstorming activities, avoid judging the merits of each cause as it is offered. Only data can lead to such a judgment.

Interpreting Cause And Effect Diagrams

Use cause-and-effect diagrams to ensure that suitable potential causes are included in the data collection and analysis. If a large majority of causes in the cause and effect chart are contained in a small number of categories, consider re-categorizing to break down the larger categories.

Learn more about the Quality Improvement principles and tools for process excellence in Six Sigma Demystified (2011, McGraw-Hill) by Paul Keller, or his online Green Belt certification course ($499).