What is a Fishbone?
A cause & effect diagram, also called Fishbone or Ishikawa Diagram, is a method to organize variables that may be a contributing factor toward causing a particular effect or contributing to your problem. A fishbone is also a way of documenting a problem’s current state and all known information. Therefore, users have a visual method to identify key causal factors for further investigation.
As seen below, the “head” of the diagram represents the “Problem Statement” box – also known as the Project Y. Along each of the spines are 6 common categories that are likely contributor categories to the project Y. Each spine contains potential contributing factors within each category, these contributors are X’s. This turns this diagram into an equation stating that your problem, Y, is a function of various factors, X.
When to Use & Why
Use a fishbone to initially identify potential causes to a problem. Additionally, if a team can no longer identify solutions, this diagram can organize factors previously examined and future opportunities.
The goal of this exercise is to document all known information about the process/challenge at hand. This information becomes potential X’s that may be contributing to the Project Y. Once identified, prioritize the X’s based on the likely impact to the problem. At this phase, use intuition and experience to determine impact. Utilize data to prove or disprove initial hypotheses when examining each factor at a later time.
How to Use
A key first step is to develop the problem definition. This is a desired characteristic, missed objective, undesired/unexpected outcome, or just the effect under investigation. This statement belongs in the box at the right side (The fish’s head).
The six categories along the backbone of the fishbone diagram to examine are,
- People: Human factors might be contributing to the problem. This may include an employee’s preference, a disability that has not been accommodated, ergonomic issues, physical limitations, etc.
- Tools: The device(s) imparting work into the process. This includes manufacturing equipment calibration and cleanliness. Using the right tool for the right job. On the specified application, is the machine operated properly?
- Environment: Factors relating to mother nature. Includes: ambient temperature and humidity, operating temperature and pressure of auxiliary/support equipment, excess wind, sunlight, or UV rays.
- Measurement: The device used to take measurements, how these measurements are taken, how many measurements are taken (repeatability of the process).
- Methods: Is process properly performed? For machinery, is equipment performing at its optimal performance?
- Materials: This is the material of a physical component and the material’s features. This may include wall thickness, proper quality, strength, toughness.
For this example, we want to identify potential contributors for a car overheating.
From the above example, we have identified multiple contributors, X’s, that may be leading to the problem, Project Y. Additionally, a number of X’s are been highlighted to indicate a high probability of that variable contributing to the cause.
Another method of prioritizing potential contributors is by utilizing a prioritization matrix like the one shown below. This will indicate which factors you and your team should focus on first by “scoring” factors based on impact to your problem statement and the ease of implementation or checking. The higher the score, the higher the prioritization.