A Comparison of Various Quality Improvement Methodologies

A Comparison of Various Quality Improvement Methodologies
Page content

Control Charts

Control Charts, developed by Walter Shewhart at Bell Labs in the 1920s is one of the earliest quality control tools. This chart plotted small production samples in a chart and measured them periodically to detect when a process was going out of “economic control.” Shewhart’s chart helped to identify whether the variability in the process is random or due to assignable causes such as poor workers or machinery. Removing assignable causes of variations restored the upper and lower limits of the process to normal levels, and brought the process back into statistical control.

Shewhart’s control charts constituted the basis for further quality improvement initiatives.

Plan-Do-Check-Act (PDCA)

The need for high quality, low-cost materials during World War II and its immediate aftermath led to an increased focus on quality improvement methods, to remove defects from assembly line manufacturing. Edward Deming a statistics professor at New York State University listed 14 points to guide companies to improve quality. He stressed on the role of top management rather than assembly line workers on improving quality, and also build on Joseph Shewhart’s Plan-Do-Check-Act (PDCA) cycle.

The PDCA and its variant Plan-Do-Study Act (PDSA) is a cyclical process that involves:

  • Determining the nature of problem, identifying the possible changes and the methodology to implement change
  • Implementing the change
  • Assessing the impact of change by establishing functional or causal relationships between changes in processes, especially behaviors and capabilities, and outcomes, and
  • Make the necessary modifications, before starting over again.

The Carnegie problem solving methodology developed by engineers at Carnegie Tech (now Carnegie Mellon University) in 1948 is similar to this PDCA cycle, but adds an additional step of defining the problem at the front. Other companies have also built on this basic model with good effects.

Juran’s Trilogy

The need for improved quality during World War II and its aftermath had many experts working. While Deming espoused his 14 points in the USA, Joseph M Juran of Japan espoused a cross-functional management approach that requires due consideration to three vital processes:

  • Quality planning, or defining the customer, identifying their needs, and developing the product or process.
  • Quality control or establishing standards of performance, measuring actual performance, and taking steps to bridge the gaps.
  • Quality improvement, or implementing improvement interventions, usually through quality teams.

Juran’s trilogy is the foundation on which the concept of Total Quality Management rests.

Value Analysis Teams

While Deming and Juran espoused their theories, Larry Miles of General Electric developed the Value Analysis Methodology that advocates the use of a formalized process to identify alternative materials, processes, and designs, to improve product functionality and reduce costs.

The major steps of such formalized process are:

  • Pre-study stages, which includes collecting customer, product, and process data, building models, and constituting multi-functional teams involving members from design, production engineering, purchasing, and quality.
  • The study stage, which involves analyzing data, brainstorming ideas, and ranking such ideas based on feasibility.
  • The post-study phase, which involves implementing and monitor changes.

Value Analysis became the precursor to the Six Sigma approach.

Quality Circles

Quality Circle

Quality Circles (QC), another Japanese invention involves workers forming teams to identify and solve process problems in their work area. Quality circles, however, had inherent limitations in that most serious quality problems arise in processes and activities that involve more than one department or function. QC has since evolved into Kaizen or continuous improvement which removes the drawback of QC by utilizing multi-functional worker and production engineering teams to improve quality and productivity. The Lean methodology makes heavy use of Kaizen.

Total Quality Management

Total Quality Management (TQM) is an integrated organizational effort designed to improve quality at every level. It involves the use of multi-functional teams to identify, analyze, and solve problems, and place special emphasis on defining quality based on how the customer perceives quality.

TQM is more a philosophy than a specific method, and incorporates in its fold, various quality measurement, control, and improvement tools. The quality teams for instance remain competent in:

  • Histograms, to see what overall variations look like
  • Scatter charts that make explicit the relationships between factors
  • Pareto analysis to identify the major problems
  • Fishbone and other cause and effect diagrams to find a root cause and identify the underlying issues
  • Process control charts that guide the variations to control.

Other methods such as Control Charts, PDCA and Juran’s Trilogy also finds its way into TQM. The quality team decides on the application of the tool best suited for the specific purpose.

Six Sigma

The Six Sigma Quality Improvement Methodology

Pioneered by Motorola and made famous by General Electric, the Six Sigma method ranks among the most popular quality management tool. It aims to reducing defects or variance in processes by applying a statistical based problem solving methodology that identifies variances from the standard mean and tries to eliminate such variances.

Six Sigma adopts a structured methodology that involves DMAIC. DMAIC is define the problem, measure, analyze, implement, and control. Comparing the baseline process capability with the actual performance or process capability helps to chalk out potential solutions for quality improvement.

Six Sigma works on the assumption that all the key underlying variables and the interactions among such variables are obvious. This need not always hold true. Design of Experiments (DoE), or experimental design is a structured and organized way of collecting multivariate data for modeling, and helps to determine whether the variables are under the full control of the experimenter.


Lean is a minimalist philosophy that aims at bringing efficiency by using the minimum required. The approach requires identifying customer needs, and improving processes by eliminating activities that do not add value to the customer. It works on the assumption that removal of waste processes improve business performance, and that many micro level small improvements are better than a comprehensive macro system analysis. It nevertheless leads to reduced flow time, process efficiency, and less inventory.

Lean works by applying:

  • Kaizen or continuous improvement to improve the process by eliminating waste
  • 5S, or the workplace organization methodology that guides how to organize the workspace for efficiency and effectiveness
  • Just in Time (JIT) inventory methods
  • Zero defect methodology… and more.

This concept introduced by Toyota in the 1950s has since then grown in popularity and scope.

The Verdict

The best quality improvement tools depend on the application. The healthcare sector, for instance requires prevention of errors or defects, for even a single defect can be fatal for a patient. This makes Six Sigma that harps on consistent products, the best possible quality tool. In contrast, a retail store offers many possibilities where consistency of output is not relevant. Here, the thrust of quality is to reduce waste and inefficiencies in the process, and methods such as Lean become relevant.

Furthermore, all quality intervention methodologies are interrelated. For instance, Kaizen teams use TQM techniques in implementing “Lean” manufacturing methods. Similarly Lean Six Sigma is a popular quality improvement tool.