What is a Fishbone?
A cause & effect diagram, also called a Fishbone and the Ishikawa Diagram, is a method to organize and test many 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, and provides a way to identify key causal factors for further investigation.
As seen in the below template of a fishbone, the challenge to be solved is listed at the “head” of the diagram in the “Problem Statement” box – this is also known as the Project Y. Along each of the spines of the diagram are 6 common categories that are likely contributor categories to the project Y. The solution team will identify potential contributing factors within each category, these contributors are known as 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
The time to use a fishbone is when you wish to seek possible causes to a problem or when your team has hit a wall and can no longer build towards identifying solutions.
The goal of this exercise is to document all known information about the process/challenge at hand, and identify 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, we’re using our intuition to determine impact, data and values to confirm or disprove our suspicions will come later.
How to Use
A key first step is to develop a specific definition of the problem to be solved. This can be 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, right-tool used for the right-job, is the machine being operated properly for the application?
- Environment: Factors relating to mother nature that could include 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 the process performed properly? If any equipment is involved, is this equipment still performing at the optimal performance?
- Materials: If you are building a widget or part of some sort, this is the material this widget is made from and the features of this material. Including wall thickness, proper quality, strength
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 have 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.