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The Seven (or so) Basic Quality Tools

Presented by Mike La DolcettaASQ Sr. Member, CQM, CSSGB

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History and Introduction

Kaoru Ishikawa

1915 - 1989

Although the Seven Basic Quality Tools were developed independently of each other, it was Dr. Kaoru Ishikawa of the University of Tokyo who popularized their use in the Quality Circles of Japan during their Quality Revolution. The original seven tools as published by JUSE in Ishikawa’s acclaimed Guide to Quality Control (1968) are:

1. Check Sheets

2. Histograms

3. Pareto Diagrams

4. Scatter Diagrams

5. Cause and Effect diagrams (aka “Ishikawa” or Fishbone Diagrams)

6. Graphs (particularly Run Charts)

7. Control Charts.

Two popular additions that will be discussed are Stratification and Process Flow Diagrams.

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Check SheetsCheck sheets can serve several functions and are typically tailored to specific needs. One of the most important is providing an organized way to collect data that lends to effective analysis. While check sheets have their roots in paper forms, the computer form shown here is a great example of a modern check sheet. This form collects quality data from the efforts of QA analysts monitoring sales reps who sell over the phone (Telesales). The QA analysts use recordings of the phone conversation between the sales rep and the customer, complete with synchronized video of the rep’s computer use during the call, to assess the sales rep’s performance on the various attributes. The results are analyzed for coaching and development of the sales force, and other endeavors.

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HistogramsA histogram is just a special type of column graph that displays frequencies or counts of something, enabling us to see how the data is distributed. The histogram below shows the distribution of QA scores for all sales reps during a specific month. A red dashed line representing the minimum passing score has been added to help us judge performance. We notice almost half of the scores are below the minimum. In fact, some reps scored zero.

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StratificationStratification, or the separation of data into different levels for analysis (in this case “tenure”), reveals that recently hired reps are struggling most with the QA process.

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Pareto Diagrams (Charts)

Joe Juran

1904 - 2008

Vilfredo Pareto

1848 - 1923

Italian economist Vilfredo Pareto stated that 80% of the wealth is controlled by 20% of the population. However it was Dr. Juran (aka the Father of Modern Quality Management) who applied this concept to quality, and designed a chart to effectively display the phenomenon that relatively few defect types typically comprise the bulk of the defectives (Juran, SP7518). The Pareto chart below reveals which QA attributes new reps failed most often, and we see that the top 3 drove over 60% of the attribute failures.

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Scatter PlotsScatter plots are typically used to check for relationships between factors. The pattern of the plotted data, as well as some calculated statistics, can expose possible cause and effect relationships. However, care should be taken to validate such relationships (for example, using designed experiments) less we be misled by undiscovered factors truly driving the results. Statistics that are often used to measure the linear strength of relationships between variables include the Pearson Product-Moment correlation and Spearman Rank correlation.

Below is plotted data for average sales revenue and average points achieved for the QA form’s sales attributes.

Karl Pearson

1857 - 1936

Charles Spearman

1863 - 1945

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Run ChartsThe basic idea behind a Run Chart is to display the trend in some attribute count or variable measure over time. Peaks are drops are readily visible on Run Charts, and can then be investigated. Below, we see historical trending of sales attribute pass rates for new reps. While stable for almost two years, performance dropped sharply for the most recent graduating class.

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Ishikawa DiagramsIshikawa’s Fishbone diagram helps us to brainstorm (typically in groups) the causes that result in the effect we are trying to understand. Major group categories along the “bones” such as Employees and Systems, etc. assist in organizing ideas for possible causal factors leading to the outcome at the “head” of the fish. Below is an example diagram for the poor sales QA scores. With possible root causes agreed upon, improvement teams can collect specific data to validate, then investigate and apply solutions.

Kaoru Ishikawa

1915 - 1989

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Process Flow DiagramsThought to have originated at Princeton University in the late 1940s to aid software development, flowcharts help us understand how processes work by using symbols and directional connecting lines to visually represent different process steps. Often when a group flowcharts an existing process, key discoveries are made and improvement opportunities are identified. The flowchart below assists in selecting the proper control chart to use based on the data involved.

Source: WHICH CONTROL CHART DO I USE? By William J. Latzko, Ph.D.www.asq.org/articles/aqc-proceedings/public_proceedings/57_2003/19375.pdf

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Control Charts

Walter Shewhart

1891 - 1967

W. Edwards Deming

1900 - 1993

Walter Shewhart (aka The Father of Modern Quality Control) introduced Control Charts in 1924s, while at Western Electric. Dr. Deming preached and popularized their use throughout both the manufacturing and services industries. The basic premise is to use statistical testing based on variation probability theory to separate process variation signal and noise (aka common cause and special cause variation) over time for process behavior monitoring and control. Different types are used depending on the nature of the data (see Which Control Chart Do I Use on asq.org). Below is a p-chart used to monitor new hire failure rate after applying solutions identified by an improvement team working the root causes identified on the Fishbone.

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SummaryHopefully these examples have provided some insights to what the Seven (or so) Quality Tools are and how they can be used for data analysis, quality improvement and quality control. Further information can be found obtained via the resources identified on the next slide. You are encouraged to think creatively to identify opportunities where you can apply these tools. And remember to share your knowledge… that’s what we’re about!

“ASQC” 1951 Exhibit- 5th National Convention

Photo from ASQ Archives: http://web.library.uiuc.edu/ahx/asq/

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References and Further ReadingClick on the hyperlinked titles to go to a web page for details (Internet connection required)

Seven Basic Quality Tools webpage on asq.org (free!)

The Certified Quality Process Analyst Handbook – Christensen, Betz, & Stein

The Quality Improvement Handbook – Bauer, Duffy, & Westcott

Juran’s Quality Handbook – Joseph M. Juran

Guide to Quality Control – Kaoru Ishikawa

Economic Control of Quality of Manufactured Product – Walter Shewhart