The Seven Basic Quality Control Tools

November 26th, 2011

Product or service quality is everyone’s responsibility, from a “Mom and Pop Shop” to an international corporation. So I thought I give those who don’t know how to look at the quality of what they do, a set of basic tools. Quality professional have all heard of “The Seven Basic Quality Control Tools” so here they are.

The Seven Basic QC (Quality Control) Tools are a given set of graphical techniques identified as being helpful in troubleshooting issues related to quality[1]. These seven are called basic because they can be used easily by anyone to solve the vast majority of quality-related issues. Many quality professional believe these were originated by Dr. Ishikawa, a world renowned quality professional.  But, he would tell you that he was inspired by the “Seven Famous Weapons of Benkei[2] . The designation as the “Seven Basic Tools of Quality” arose in postwarJapan.

The Tools

  1. 1.      Cause and Effect Diagrams: (Fishbone Diagrams, Ishikawa Diagrams)

These diagrams are tools that organize a group or persons knowledge about the causes of a problem or issue and display the information graphically.

 

It was originally created and used by Dr. Kaoru Ishikawa and is sometimes called an Ishikawa Diagram. Also, because of its shape it is called a Fishbone Diagram. In general what you do is brainstorm ideas (causes) then group them in to categories. Those categories become the many branches of the Cause and Effect diagram.

  1. 2.      Check Sheets:

This is another simple but powerful tool. Check Sheets are lists of items and the frequency that the item occurs. They can be made in so many different ways that many times, we don’t think of them as a list, but they are. below are two, one that kind of looks like a list the other not so much. On the shoe the defects are marked with an “x” in the location it was found.

They are use to answer many important questions such as:

  • Has all the work been done?
  • Has all the inspection been done?
  • How frequently a problem occurs?

They are often used to remind individuals doing complex tasks of what to do and in what order. They are also used many times in conjunction with other tools to help quantify or validate information.

  1. 3.      Control Charts:

Control charts are the most difficult of the seven tools to use. They are seldom the method  of choice. When a process step is important, we would prefer that the step not vary at all. ONLY when this can not be accomplished in an economical way does one choose to use a control chart. Below is an “XBar-R Chart” also called an “Average and Range Control Chart”.

Control charts are only useful if the step (operation or function), over time, exhibits measurable random variation. Control charts display the data over time (Time is on the x axis above listed as sample). Control Limits (the red lines) are displayed on control charts, where data falling within the control limits are considered “normal” variation. Any point outside the control limits are considered “special caused” variation and need to be look at and corrected through an action plan. If you create a control chart, you must also have with it an action plan.

Besides control limits for control charts, there are several other type of trends (runs) that can indicate an out-of-control process.

What I have shown above is only one type a control chart and one of the simplest to use but there are several others (not so simple to use). Below is a Decision Tree Diagram of the different type and there use. Be sure you understand the application of each control chart or get help if you plan to use one of these.

  1. 4.      Histograms:

Histograms are a “picture” of a set of data (or information). It is created by grouping the data you collect in to “Cells” or “Bins” (Bars in the chart below).

Histograms take your data and give it a shape (Distribution). With this, you can see the data sets spread, central tendencies, and if it meets requirements. As you can see, it is a valuable troubleshooting tool. You can take it a compare differences between machines, people, suppliers etc. Never use a histogram alone always also plot it in a time ordered  plot (run chart).

  1. 5.      Pareto Charts:

Pareto Charts are a specialized Histogram of count data. It arranges the Bins or Cells in largest to smallest counts and gives you an accumulation line as seen below.

The Pareto Chart gets its name from the use of the Pareto Principle which states “ 80% of the effect comes from 20% of the causes”. Vilfredo Pareto, an Italian economist, originated this principle by determining that 80% of the land inItalyis owned by 20% of the population. Later it was found to hold true in many things and help us focus on the critical few. With a chart like this a team can decide where to place its priority and focus ( the big hitters). This is extremely helpful when time and money is limited as it is in most cases.

  1. 6.      Scatter Diagrams:

Scatter plot are a very simple tool to use to see if there is a correlation between two things (i.e. does one thing lead to another). I always before going into any major analysis of data, plot the data in some way to get a “gut feel” of what is happening. This tool lets you create a simple picture showing how two or more variables change “together”.

As one can see in the chart above the fruit on the tree increase in weight the longer it is on the tree. In scatter charts we see if one thing relates (correlates) with another. Below is a set of chart that shows some of the relationships you might find with this tool.

  1. 7.      Stratification: (Flow Charts, Run Charts, etc.)

To me Stratification is a catch-all for summarizing, picturing, or applying some tool to data so you can understand what is happening. Stratification is the process of dividing members of a population into homogeneous subgroups before using it. The data (strata) should be mutually exclusive: every element in the population must be assigned to only one subgroup (stratum). The data should also be collectively exhaustive: no population element (data) can be excluded.

That’s a mouthful, but if you look at above six tools all of them do this stratification of the data. In many texts they list either flow charts or run charts under this seventh tool area. A run chart is just the “Individuals Chart” of the above control chart without control limits. A flow chart takes a group of steps in a process and summaries them into a map of the way the process works. They are sometimes called a Process Map or a Process Flow Map.

They are created to:

  • Create a common understanding of the process flow
  • Clarify steps in a process
  • Uncover problems and misunderstanding in a process
  • Reveal how a process operates (good and bad)
  • Helps you ID places for improvement.

Well there you have a short description of the Seven Basic Quality Tools. Stay in touch as I go into each tool with details of how to construct and interpret them. If, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.

Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090



[2] Ishikawa, Kaoru (1990), Introduction to Quality Control (1 ed.), Tokyo: 3A Corp, p. 98, ISBN 9784906224616, OCLC 23372992

 


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8 Responses to “The Seven Basic Quality Control Tools”

  1. Very nice. I personally like to expand the “classic “Checksheet” (Tool #2) to include a data collection plan required for the regression / correlation (tool #6).

    Dave

  2. [...] and Effect Diagram (C&E Diagram), sometimes called the Fishbone or Isjikawa Diagram, is one of the Seven Basic QC Tools. It is a simple but effective way to organize a group or persons knowledge about the potential [...]

  3. [...] histogram, one of the Seven Basic QC Tools,  is a very good tool to use to picture what a set of data looks like.  It give shape to a set of [...]

  4. [...] plots are one of the Seven Basic QC Tools. They are a graph showing you the relationship between two factors or variables. It can show you if [...]

  5. [...] Pareto Charts are a specialized Histogram of count data. It arranges the Bins or Cells in largest to smallest counts and gives you an accumulation line as seen below. It is one of the Seven Basic Quality Tools. [...]

  6. [...] charts are the most difficult of the seven basic quality tools to use. They are seldom the method of choice. When a process step is important, we would prefer [...]

  7. I do accept as true with all of the ideas you’ve introduced on your post. They are very convincing and will definitely work. Still, the posts are very brief for beginners. Could you please prolong them a little from subsequent time? Thanks for the post.