When you’re trying to find a solution to a business problem, such as a manufacturing quality issue, a root cause analysis (RCA) is usually the right way to go. But there are a number of different RCA techniques which can be applied. Some examples include:
- Pareto Chart
- Fishbone Diagram (or cause and effect diagram)
- Scatter Plot Diagram
- 5 Whys
- Fault Tree Analysis
- Failure Mode and Effect Analysis (FMEA)
In this blog, we’ll focus on Pareto charts and fishbone diagrams. Both help to diagnose the root causes of quality issues rather than focus on the symptoms alone. But when and how are they used? Let's find out.
What is a Pareto chart?
A Pareto chart is a quality management tool that provides a way to visualize business problems, analyze them, and come up with ways to improve things. Pareto charts are based on the Pareto principle, also known as the 80/20 rule as it states that 80% of consequences occur as a result of 20% of the known causes.
A Pareto chart resembles a bar chart combined with a line graph. It identifies the different components or aspects of a quality issue and puts them in descending order from the one that has the most impact to the lowest impact.
Pareto Chart Quality Management Benefits
A Pareto chart is most commonly used to break down quality issues into component problems or groups of problems and analyze the frequency of them. The goal is to highlight the most significant quality issues, allowing them to be addressed in priority order.
Pareto charts can help to:
- Analyze manufacturing processes and zero-in on specific inefficiencies
- Reduce the complexity of quality management issues
- Communicate quality issues to a team in a visual way
- Prioritize problems and set a plan of action to rectify them
How to create a Pareto chart
To create a Pareto chart, you should follow these steps:
- Group the problems into categories
- Decide the type of measurement – e.g. frequency, quantity, time, cost
- Decide upon the time period – e.g. one day, one week, one work cycle
- Gather the data
- Add the data to the chart
In the example below, we have created a Pareto chart using AlisQI. The 8 main inconsistencies when manufacturing pickles have been analyzed in terms of frequency, with bitter being the most common and spotted pickles the least common.
On a Pareto chart, these eight defects appear on the X-axis. The Y-axis states the frequency for each inconsistency and orders them from the most to the least frequent. Prioritizing the largest bars, the defects that occur most often will help with overall improvement more than focusing efforts on the shorter bars.
The Z-axis, to the right, represents the cumulative percentage or the percentage of defects that can be removed if the most frequent types of defects are resolved. A steep line in your cumulative percentages indicates causes that have a more significant impact.
Limitations of the Pareto chart
While the Pareto chart can be a very useful tool for manufacturers, you also need to bear in mind that it:
- Provides a high-level overview of the quality issue causes, not an in-depth analysis
- Only displays qualitative data without revealing the severity of each cause
- Uses historical data only, with no real-time data
- Might include potential data inaccuracies, depending on how that data was collected.
What Is A Fishbone Diagram?
A fishbone diagram is a basic root cause analysis tool which is sometimes referred to as an Ishikawa or cause-and-effect diagram. The purpose of a fishbone diagram is to highlight all the possible causes of any given quality problem.
Fishbone diagram quality management benefits
A fishbone diagram is a highly visual way to gain a clearer perspective of quality-related issues and problems, allowing for more in-depth analysis. Other benefits of using a fishbone diagram include:
- Uncovers the granular causes of a quality issue
- Helps to simplify quality analysis for complex processes and workflows
- Facilitates the brainstorming of the causes of quality problems
- Assists with quality problem solving and decision making.
How to create a fishbone diagram
To create a fishbone diagram, the following steps should be followed:
- Write down a problem statement.
- Draw a horizontal line or arrow to the left of the problem statement.
- Brainstorm the causes of the main problem as categories.
- Draw diagonal arrows or lines to resemble branches spreading out from the horizontal arrow and write a different category at the end of each one.
- Brainstorm the causes within each category – asking “why do the problems occur in this category?” to generate sub-categories.
- Draw an arrow branching from the category arrow and write down the sub-category on the smaller arrow.
- Brainstorm and add any further causes if you or other team members think of any.
- Continue this process until you are out of sub-categories and causes to add to the diagram.
The fishbone diagram below shows the overall problem statement of a manufacturer ending up with an inconsistent product. The brainstorming process identified six sub-categories – method, machine, man, material, measurements and mother nature. Within each sub-category, further causes can be added as branches.
Limitations of a fishbone diagram
While a visual representation can provide more perspective, manufacturers should also be aware that:
- Brainstorming ideas can lead to a large number of potential causes, with some being irrelevant due to minimal impact
- The diagram is more complicated to view and understand than a Pareto chart
- The sheer amount of categories and sub-levels can make the problem seem bigger than it really is or make the solution appear impossible to achieve – therefore, the process of creating a fishbone diagram needs to be carefully managed to avoid demoralizing your team.
Should you use a Pareto chart or a fishbone diagram?
Choosing between a Pareto chart and a fishbone diagram is relatively simple.
- Prioritization – If you’re looking to prioritize the causes of the quality problem you want to address, and the frequency of each cause can be easily measured and recorded, then a Pareto chart may be the best choice.
- In-depth analysis – If you want to dig deep into the root causes of the quality issue and uncover granular detail about potential causes, then a fishbone diagram may be best. If the frequency of the causes is difficult or impossible to measure, then a fishbone diagram may also be suitable as a root cause analysis tool.
Drive continuous improvement efforts with a no-code quality management system
Quality Management software helps you to save time by cutting down on manual tasks in root cause analysis. Automate data collection and processing, and identify opportunities straight away. Discover how AlisQI can help to streamline your continuous improvement – book a demo today.