Quality control experts lean heavily on the so-called “7 Basic Tools of Quality” to fine-tune processes as part of an overall quality assurance effort.
It’s said that these basic quality assurance tools were first emphasized by Karou Ishikawa, a Japanese organizational theorist who’s credited as a heavyweight in quality management and is especially known for the development of the quality circle and Ishikawa, or fishbone, diagram, which is itself one of the 7 basic tools we’ll talk about in this article. As is often the cause in quality, you can also detect the influence of W. Edwards Deming on the 7 basic tools.
The 7 tools are graphing techniques that are very helpful for, and commonly used, for quality control troubleshooting purposes.
So let’s start learning about these very useful techniques for quality control.
7 Basic Tools of Quality
You can use the 7 basic tools of quality to help understand and and solve problems or defects in any industry.
Conveniently, the tools are simple to use and don’t require a lot of expertise in statistics. That’s even more true since software programs can now be used to create the graphs and diagrams once given the data.
Knowing how to use these tools, and actually using them, will give you a big help in terms of solving the problems you face at work on a daily basis.
Quality Tool 1: The Cause-and-Effect Diagram (also known as Ishikawa Diagram and/or Fishbone Diagram)
An Ishikawa diagram is also known as a fishbone diagram (because it looks like a simple depiction of a fish skeleton) or a cause-and-effect diagram (because it’s often used to show the cause of a specific event, though it’s also used for product design).
People often use cause-and-effect diagrams to determine the cause of an event, to brainstorm possible causes of a problem, or to design a product,
The “fish” of an Ishikawa diagram is always drawn with the “head” of the fish pointed to the right. The head represents the problem or cause. The “bones” of the fish branch off the central, horizontal spine and angle to the left. Each bone represents a possible major cause of the event. There can be smaller bones branching off each major bone to represent related sub-causes.
The 6M design is commonly used for cause-and-effect diagrams analyzing production processes. In 6M, the potential major causes are:
- Mother nature (environment)
- Manpower (people)
The 6M cause-and-effect diagram doesn’t work for every situation, but it can be a helfpul way to begin organizing thoughts for many. For other problems, you may need to come up with your own causes.
Because it seems that nothing’s ever simple and easy, you will sometimes seen this listed as the 5 Ms (machine, method, material, man, measurement) and even see it sometimes expanded to 8 Ms (including mission, mother nature, management, and maintenance). Use what works best for each scenario.
Quality Tool 2: The Check Sheet
A check sheet is a sheet or form used to collect and then later analyze data. It is typically created at the point where the data is created (such as at the end of a production line).
Check sheets are often used to collect data on the frequency, location, or even cause of problems or defects during production.
The basic idea is that the check sheet is divided into a number of different regions, and data is then marked into the different regions using a mark to check to indicate something.
In general, a check sheet will include headings that provide the following information:
- Who recorded the data on the check sheet
- What each check or mark on the check sheet represents (for example, the type of defect or problem)
- The location at which the data was collected
- When the data location occurred
- Why the data on the check sheet was collected
Using Check Sheets to Keep Track of the Completion of Steps in a Multi-Step Procedure
Check sheets are often used to describe the results of a procedure, as explained above.
However, they can also be used to keep track of the completion of the different steps of a procedure. In this case, the check sheet is often known as a checklist.
The checklist concept is all about creating a list of procedures for a worker to follow so he/she won’t make a mistake. This type of check sheet is especially useful during multi-step procedures, and in quality it’s often used when checking and finishing process outputs (although again, it can be used while creating outputs as well).
For more about checklists, you may also want to check out:
- Checklists and the Convergence LMS
- Atul Gawande’s Checklist Manifesto
- Free Downloadable Operational & Safety Checklists
You may also be interested to learn more about mobile digital tools for checklists, such as the one shown below.
Quality Tool 3: The Control Chart
Process control charts track the values of a process over time. The vertical dimension will usually represent a process value or measurement, while the horizontal dimension will usually represent how often or when the measurement was taken. Control charts are very useful for analyzing and reducing variation in a process, and they can be used to determine if a process is “in control” or not.
Control charts are also sometimes known as Shewhart charts (after Walter A. Shewhart) or process-behavior charts.
There are different types of control charts for different types of data, but all control charts have a center line that represents the average or mean and two parallel lines that represent the upper and lower control limits. This concept is briefly explained in this short sample from our online process control charts training course, below.
There are several conditions that indicate the process is out of control, including at least one point outside the control limits or nine points in a row on the same side of the centerline.
Here are some examples of how process control charts might be used at production facilities:
- A paper manufacturer might track the thickness of their paper.
- A pizza company might track how many pepperoni are on their pizzas.
- A power company might track the amount of energy being produced.
Every production process has many sub-processes. Because process control charts only chart a single value, every production process can have many process control charts.
A process control chart can be used to measure a wide range of process behaviors such as:
- Product values – For example, the number of pepperoni on each slice of pizza
- Defect rates – For example, the number of defects per hour or the number of defects per 100 samples
- Deviation – For example, the difference between the previous measured value and the current measured value
- Non-physical processes – For example, the amount of time it took for a product to go from concept to production
Quality Tool 4: The Histogram
A histogram is a graph that used to show how often a value, or range of values, occurs in a given time period. Histograms provide a visual summary of large amounts of variable data. The shape of the distribution can tell you a lot about the data set. Using a histogram, you can tell if:
- How data is distributed, including if it’s normally distributed
- The process is capable of meeting customer requirements
- Changes have occurred in the process, or
- How two processes compare
For histograms to provide meaningful data, you need at least 50 data points divided into 6-10 intervals, or bins.
To create a histogram, start by determining the intervals or “bins” that represent the range of values, then determine how many values fall into each bin. The bins are typically consecutive, non-overlapping, and of the same size (though that last one isn’t required).
Once all the values are plotted into the bins of a histogram, the patterns of the histogram are described as:
- Skewed left
- Skewed right
Histograms were first introduced by Karl Pearson.
Quality Tool 5: The Pareto Chart
A Pareto chart is a chart that includes bars and a line graph. Pareto charts are based on the Pareto principle, or 80/20 rule, which states that roughly 80% of the effects are caused by 20% of the problems, and are named after Vilfredo Pareto.
The vertical axis on the left often represents the frequency of occurrence. The right vertical axis represents the cumulative percentage of the total number of occurrences.
Each bar in a Pareto chart represents the relative frequency or magnitude of a problem or cause, and the bars are arranged in descending order (with the longest or tallest on the left, and the shortest on the right). And the line graph shows the percentage of total data included up to that problem category.
Arranging the bars in this way allows you to visually identify the most significant data groups, which is especially useful for prioritizing work on the most significant problems. In quality control, the Pareto chart is often used to represent the most common sources of defects, the most frequent types of customer complaints, and similar issues.
Quality Tool 6: The Scatter Diagram
Scatter diagrams are also called scatter graphs, scatter charts, scatter plots, and even scattergrams. Scatter diagrams are often used to help understand how variables are related and to identify root cause.
A scatter plot is a graph of paired numerical data samples. The independent variable is plotted along the horizontal x-axis and the dependent variable is plotted on the vertical y-axis. You can then draw a trend line to study the relationship between the variables
The closer the data points fall along the trend line or curve, the stronger the relationship and the more likely it is that a change in one variable will change the value of another variable. Scatter plots are often accompanied by regression analysis, which quantifies the strength of the relationship between the two variables and can be used to predict future values.
Scatter diagrams can be built as:
- Bubble charts
- Marker charts
- Line charts
Quality Tool 7. Stratification (also known as Flow Chart and/or Run Chart)
Stratification is a method of organizing data. It’s the process of separating data into meaningful groups. Stratification is also known as a flow chart or run chart.
Each data point should be included in only one group, and no data point should be left out.
Once you’ve separated the data into groups, you can then compare the groups and see the effects of the grouping variables.
Typical stratification groups used for quality control purposes include:
- Who – the people involved with the problem. For example, which operator or crew was working at the time
- What – machines, products, raw materials or any other objects relevant to the problem
- Where – a process area, physical location, or a location on a machine or product
- When – time of day, day of the week, shift, or process step when the problem occurs
Conclusion: 7 Basic Tools of Quality
We hope you found some useful information about quality control and learned some helpful quality control tools in this article about the 7 basic tools of quality.
Keep your eye on our blog for future articles looking at each tool in more depth, plus additional articles about quality control and quality assurance tools and techniques.
Also know that we’ve got an upcoming online 7 basic quality tools course that’s currently in production and will be ready for you to buy soon. It’s just another new title in our online manufacturing training courses library.
Let us know if you’ve got any additional questions. Otherwise, we’ll catch up with you again at our next article.
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