Using a Fishbone Diagram for Root Cause Analysis

A fishbone diagram is a tool used to facilitate root cause analysis for a defined problem. The diagram provides a structured way to record potential root causes during brainstorming, encouraging teams to think about a problem systematically and to dig deeper to discover less obvious causes.

The fishbone diagram is a type of cause and effect diagram. It is also referred to as an Ishikawa diagram after Dr. Kaoru Ishikawa, the Japanese quality control expert who invented it. The popular name, “fishbone” stems from the fact that the diagram resembles the skeleton of a fish.

Fishbone analysis begins with a situation to be studied. The dilemma is written down in question form on the right hand side of a page. Then, an arrow, or occasionally a depiction of a fish head, will point to the predicament to be studied. Off to the left of where the dilemma is stated, a horizontal line splits the paper into to sections. This forms the “backbone” of the fishbone diagram.

The next set of bones represents the most important categories of the factors which might lead to the basic cause; the names of these categories are written along the top and bottom of the paper, with angled arrows pointing back to the backbone as well as towards the head, thus forming a herringbone pattern.

Conventions have developed to provide starting categories appropriate for different types of problems domains. In manufacturing, the 6 M’s are used: Machine, Methods, Materials, Maintenance, Man, and Mother Nature. Modern analysis of manufacturing problems adds categories like: Equipment, Process, People, Materials, Environment, and Management. The 8 P’s are a useful starting point for analysis of service and administrative problems: Price, Promotion, People, Processes, Place / Plant, Policies, Procedures, and Product. A service industry may also use the 4 S’s: Surroundings, Suppliers, Systems, and Skills.

Analysis gets underway after the fundamental skeletal structure is in position. Variables are listed that play a part in each subset of elements that result in the underlying or root cause. These are displayed on top of arrows directing you to the subset lines, which themselves may possess lines of their own directing toward them, further delineating the variables that play a part. While this may proceed ad infinitum, naturally it will be hard to sketch more than a minimal number of levels.

As the skeleton of the diagram comes together, the team begins to brainstorm and look for solutions to the outlined problem. It is often helpful that the problems be phrased in the form of a question, such as, “Why is this happening?” and “What issues are contributing to this complication?” Team members can be asked to answer these questions in the context of each category of problems.

For alternative options to be analyzed and final decision is concluded, meeting process of the team members is continued. After thorough discussion, the main reason for the problem is identified in the meeting. It is quite probable that one reason may lead to various issues and concerns in the organization. Similarly, we can say that common reasons which lead to various issues shall be significant enough for analysis.