and the overall business strategy, is unique to Six Sigma. In addition, the emphasis on reducing the variation in a process is a relatively new concept. Earlier quality efforts may have emphasized aligning processes to desired target levels but did not necessarily reduce the variation around those targets. Taguchi’s work in the 1980s introduced the importance of reducing variability to improve quality and reduce quality costs.
Finally, the requirement that quality improvement be tied directly to the organization’s bottom line is a distinct hallmark of Six Sigma. Six Sigma projects saved GE a reported $12 billion over five years (5). Results such as these have earned Six Sigma enduring popularity with executives.
2.4 Quality Tools Used in Six Sigma
The quality tools available to Six Sigma practitioners are vast. For example, The Quality Toolbox by Nancy Tague details over 100 separate tools that can be used in project planning, idea creation, process analysis, data collection and analysis, cause analysis, and decision making. The statistical tools used in Six Sigma projects include:
Hypothesis testing
Analysis of variance (ANOVA)
Gauge repeatability and reproducibility (R&R)
Statistical control charts
Process capability
Correlation and regression analysis
Design of experiments
Multivariate analysis
Time‐series analysis
2.4.1 The Basic Seven Tools and the New Seven Tools
Six Sigma practitioners also leverage the Basic Seven and New Seven Tools. The Basic Seven tools were first brought into focus by Kaoru Ishikawa, a professor of engineering at Tokyo University and the father of “Quality Circles.” These tools can be used to collect and analyze data in the Measure, Analyze, Improve, and Control phases of a Six Sigma project:
1 Cause‐and‐effect diagram (also known as Ishikawa or fishbone diagram): A visual tool that identifies potential causes of a problem and sorts ideas into useful categories.
2 Check sheet: A structured, prepared form for collecting and analyzing the frequency of occurrences of various events.
3 Control chart: A graph used to study how a process changes over time. Comparing current data to historical control limits leads to conclusions about whether the process variation is consistent (in control) or unpredictable (out of control due to some special causes of variation).
4 Histogram: A bar chart that shows the shape of a data set using its frequency distribution, or how often each value occurs in a data set.
5 Pareto chart: A bar graph that shows the frequency of occurrence of events in descending order. The chart helps the team focus on the main drivers of a problem.
6 Scatter diagram: An X‐Y plot that shows the relationship between two quantitative variables that are measured in pairs.
7 Stratification: A technique that separates data gathered from a variety of sources so that patterns can be seen.
All of these tools are discussed at length in the next three chapters.
In 1976, the Union of Japanese Scientists and Engineers (JUSE) saw the need for tools to promote innovation, communicate information, and successfully plan major projects. A team researched and developed the New 7 Tools, often called the Seven Management Tools:
1 Affinity diagram: A visual tool that allows a team to organize a large number of ideas, opinions, or issues into their natural relationship groupings.
2 Arrow diagram: A graphical tool that shows the required order of tasks in a project or process, the best schedule for the entire project, and potential scheduling and resource problems and their solutions.
3 Interrelationship diagram: A visual tool that shows cause‐and‐effect relationships and helps analyze the natural links between various aspects of a complex situation.
4 Matrix diagram: A tool that shows the relationship between two, three, or four groups and can give information about the relationship, such as its strength and the roles played by various individuals or measurements.
5 Prioritization matrix: A decision tool that rates various options based on predetermined criteria.
6 Process decision program chart: A risk analysis tool that systematically identifies what might go wrong in a plan under development.
7 Tree diagram: A visual tool that breaks broad categories down into finer and finer levels of detail, helping to move step‐by‐step thinking from generalities to specifics.
2.4.2 Lean Tools
Recently, the Six Sigma methodology has been enhanced by incorporating the tenets of Lean Thinking. The Lean philosophy places importance on mapping the value stream and stresses the elimination of waste and continuously improving processes. Lean tools such as Eight Wastes, visual management, the 5S method, value stream mapping, mistake‐proofing, and quick changeover have become powerful tools used in the Improve and Control phases of Six Sigma projects. Together, Six Sigma and Lean deliver higher quality, increased efficiency, and flexibility at a lower cost.
The Lean philosophy follows five principles. First, we specify value, as perceived from the end user’s point of view. Next, we identify the value stream, which includes all the activities performed from the time of customer order to delivery. Every task we perform can be classified as value‐added or non‐value‐added. Third, we create flow so that our product – parts or paperwork or information – moves through the system without any hiccups. Fourth is the idea of pulling from the customer, meaning that we will make a product when a customer orders it, as opposed to making products that sit in inventory. Finally, we seek 100% quality and perfection in our operations. Contrast this to the Six Sigma goal of 3.4 DPMO, which is the result after the 1.5σ shift. The Lean goal of perfection lends itself to the idea of continuous improvement: we can always do better; we are never done; we will never quite reach the goal.
Non‐value‐added activities or policies are classified as waste. In Lean, there are Eight Wastes, and the goal is to identify and eliminate this waste. This contrasts with Six Sigma, in which we try to reduce variability.
2.4.2.1 Eight Wastes
As we have noted, the emphasis of Lean is on reducing waste, and there are eight named wastes: transportation, inventory, motion, waiting, overproduction, over‐processing, defects, and skills (TIM WOODS). These wastes do not add value to the product or service and should be eliminated. We’ll now define each of them.
Transportation waste is the movement of things, whether actual materials, paperwork, or electronic information. Moving things from place to place does not add value to the product or service. In fact, there is a higher probability of parts getting lost or damaged, the more we move them. There might
