In 1950, the Japanese Union of Scientists and Engineers (JUSE) invited legendary quality guru W. Edwards Deming to go to Japan and train hundreds of Japanese engineers, managers and scholars in statistical process control. Deming also delivered a series of lectures to Japanese business managers on the subject, and during his lectures, he would emphasize the importance of what he called the “basic tools” that were available to use in quality control.
One of the members of the JUSE was Kaoru Ishikawa, at the time an associate professor at the University of Tokyo. Ishikawa had a desire to ‘democratize quality’: that is to say, he wanted to make quality control comprehensible to all workers, and inspired by Deming’s lectures, he formalized the Seven Basic Tools of Quality Control.
Ishikawa believed that 90% of a company’s problems could be improved using these seven tools, and that –- with the exception of Control Charts — they could easily be taught to any member of the organization. This ease-of-use combined with their graphical nature makes statistical analysis easier for all.
The seven tools are:
- Cause and Effect Diagrams
- Check sheet
- Control (Run) Charts
- Pareto Charts
- Scatter Plots
- Flow Charts
What follows is a brief overview of each tool.
Cause and Effect Diagrams
Also known as Ishikawa and Fishbone Diagrams
First used by Ishikawa in the 1940s, they are employed to identify the underlying symptoms of a problem or “effect” as a means of finding the root cause. The structured nature of the method forces the user to consider all the likely causes of a problem, not just the obvious ones, by combining brainstorming techniques with graphical analysis. It is also useful in unraveling the convoluted relationships that may, in combination, drive the problem..
Also known as Data Collection sheets and Tally charts
Check sheets are non-statistical and relatively simple. They are used to capture data in a manual, reliable, formalized way so that decisions can be made based on facts. As the data is collected, it becomes a graphical representation of itself. Areas for improvement can then be identified, either directly from the check sheet, or by feeding the data into one of the other seven basic tools.
Control (Run) Charts
Dating back to the work of Shewhart and Deming, there are several types of Control Chart. They are reasonably complex statistical tools that measure how a process changes over time. By plotting this data against pre-defined upper and lower control limits, it can be determined whether the process is consistent and under control, or if it is unpredictable and therefore out of control.
Histograms are a form of bar chart. They are used to measure the frequency distribution of data that is commonly grouped together in ranges or “bins”. Most commonly they are used to discern frequency of occurrence in long lists of data. For instance, in the list 2, 2, 3, 3, 3, 3, 4, 4, 5, 6, the number 3 occurs the most frequently. However, if that list comprises several hundred data points, or more, it would be difficult to ascertain the frequency. Histograms provide an effective visual means of doing so.
Based upon the Pareto Principle that states that 80% of a problem is attributable to 20% of its causes, or inputs, a Pareto Chart organizes and displays information in order to show the relative importance of various problems or causes of problems. It is a vertical bar chart with items organized in order from the highest to the lowest, relative to a measurable effect: i.e. frequency, cost, time.
A Scatter Diagram, or Chart, is used to identify whether there is a relationship between two variables. It does not prove that one variable directly affects the other, but is highly effective in confirming that a relationship exists between the two.
A flow chart is a visual representation of a process. It is not statistical, but is used to piece together the actual process as it is carried out, which quite often varies from how the process owner imagines it is. Seeing it visually makes identifying both inefficiencies and potential improvements easier.
The seven basic tools of quality can be used singularly or in tandem to investigate a process and identify areas for improvement, although they do not all necessarily need to be used. If a process is simple enough – or the solution obvious enough – any one may be all that is needed for improvement. They provide a means for doing so based on facts, not just personal knowledge, which of course can be tainted or inaccurate. Ishikawa advocated teaching these seven basic tools to every member of a company as a means to making quality endemic throughout the organization.