Process improvement methodologies: 9 methods compared

Process improvement methodologies are structured approaches for making work faster, cheaper, safer or more reliable. The main ones are PDCA, lean, kaizen, Six Sigma, Lean Six Sigma, TQM, theory of constraints, reengineering and Agile retrospectives. Each answers a different kind of problem.

This guide defines process improvement, then covers each method with its origin, where it fits and a short example. It ends with how to choose between them and how to combine them.

Key takeaways

Process improvement means studying how work gets done and changing it so the results get better.

Match the method to the problem: waste and delay, variation, a bottleneck, or a broken design.

Continuous improvement methodologies such as PDCA and kaizen make many small changes, while reengineering makes one large one.

Most organizations combine methods, using one as the cycle and others as tools inside it.

Every example in this guide is illustrative, not a documented company result.

What is process improvement?

Process improvement is the practice of analyzing how work flows and changing it so that quality, speed, cost or safety gets better. To define process improvement simply: understand the current process, find the problem, change it, and check that the change worked.

A process here means any repeatable chain of steps, from machining a part to approving an invoice. Continuous process improvement methodology adds one idea: the work never stops, so improvement repeats.

The continuous improvement page covers that ongoing habit in more detail.

PDCA and kaizen: the continuous improvement core

PDCA is a four-step cycle of plan, do, check and act, and kaizen is the habit of running such cycles every day. Together they form the base of most continuous improvement methodologies.

Walter Shewhart described the cycle in his 1939 book Statistical Method from the Viewpoint of Quality Control, and W. Edwards Deming promoted it, which is why it is also called the Deming cycle. Masaaki Imai's 1986 book Kaizen: The Key to Japan's Competitive Success brought kaizen to a wide audience.

Good fit: small, frequent changes by the people doing the work. Say a team trials a new tool layout for one week, checks the walking distance and then adopts or drops it. See the PDCA method and the kaizen event guide.

Lean: removing waste and improving flow

Lean is a way of improving processes by removing waste so that value flows to the customer without delay. It grew out of the Toyota Production System.

John Krafcik used the term lean in a 1988 article. Womack, Jones and Roos popularized it in their 1990 book The Machine That Changed the World. Womack and Jones followed with Lean Thinking in 1996.

Good fit: processes with long waits, rework, excess stock or unclear flow. Say an order sits in three queues before shipping. A value stream map shows the touch time is a small part of the lead time. The lean tools library lists the methods used.

Six Sigma, DMAIC and Lean Six Sigma

Six Sigma is a data-driven method for reducing variation and defects, usually run as DMAIC projects: define, measure, analyze, improve and control. Lean Six Sigma combines it with lean waste removal.

Six Sigma was developed at Motorola in the 1980s, and engineer Bill Smith is often credited with its origin. Michael George's 2002 book Lean Six Sigma: Combining Six Sigma Quality with Lean Speed helped establish the combined approach.

Good fit: a stable process that produces inconsistent results and where data can be collected. Say a filling line gives uneven volumes, and a DMAIC project finds which factor drives the spread. See DMAIC and lean vs Six Sigma.

Total quality management (TQM)

Total quality management is an organization-wide approach in which every function and every employee takes responsibility for quality and customer satisfaction. It focuses on culture and management practice more than on a single tool.

The ideas grew from the work of Deming, Joseph Juran and Armand Feigenbaum, and the term became common in the 1980s. Good fit: organizations that want a shared quality culture, with leadership commitment and customer focus as the base.

An example: a hospital laboratory sets quality goals for every team, reviews customer complaints monthly and trains staff in basic problem solving.

Theory of constraints

The theory of constraints says that every system has one limiting step, and improving anything else will not raise output. You find the constraint, get the most from it, then move to the next one.

Eliyahu Goldratt introduced it in his 1984 novel The Goal. Good fit: a process with a clear bottleneck, where work piles up in front of one step.

Say a print shop's finishing machine handles 50 jobs a day while upstream steps could do 80. Adding capacity upstream changes nothing, but a faster finishing step raises output.

Business process reengineering

Business process reengineering is a radical redesign of a process from a blank sheet, aimed at a large jump rather than gradual gains. It questions why the work is done at all.

Michael Hammer set out the idea in his 1990 Harvard Business Review article Reengineering Work: Don't Automate, Obliterate. He and James Champy expanded it in the 1993 book Reengineering the Corporation.

Good fit: a process that is broken by design, such as a ten-step approval chain built around old paperwork. The risk is disruption, so it suits rare, large changes. Compare it with the small steps in kaizen.

Agile retrospectives

An Agile retrospective is a regular team meeting that reviews how the work went and picks one or two changes to try next. It is process improvement on a short cycle for software and knowledge work.

The Agile Manifesto principles of 2001 say the team reflects at regular intervals on how to become more effective. Esther Derby and Diana Larsen's 2006 book Agile Retrospectives gave teams a practical format.

Good fit: teams working in short iterations. Say a team notices reviews wait two days, and agrees to pair on reviews for the next sprint. See the retrospective tools category.

How to choose a process improvement methodology

Choose a methodology by naming the type of problem first. Waste and delay point to lean, and variation points to Six Sigma. A bottleneck points to theory of constraints, and a broken design to reengineering.

For many small, everyday problems, use PDCA and kaizen. For a quality culture across a whole organization, TQM gives a framework. For a team that works in iterations, use retrospectives.

Also weigh data and time. DMAIC needs reliable data and weeks of effort, while a PDCA trial can start tomorrow. The operational excellence software category lists tools for tracking such programs.

How to combine methodologies

Combine methodologies by using one as the improvement cycle and the others as tools inside it. PDCA often works as the cycle, with lean mapping to find waste and DMAIC statistics to confirm causes.

A practical sequence: map the process, find the constraint, run a focused kaizen event on it, then use DMAIC if variation remains. Reserve reengineering for processes that small changes cannot fix.

Keep the combination simple. One shared language and one improvement cycle are better than three methods run by three separate teams.

Frequently asked questions