Lean, Six Sigma and Theory of Constraints

Process improvements. Which should I use? Lean, Six Sigma or TOC?

There is an ongoing debate between consultants on which is better – lean, six sigma or TOC (theory of constraints). There is a tendency to use baffling jargon – often in japanese – and overcomplicate things. In reality most continuous improvement tools are similar, just with different focuses:

  • Lean focuses on minimising waste.
  • Six Sigma focuses on minimising variation.
  • Theory of Constraints focuses on reducing bottlenecks.

An approach that usually works is to use TOC to help you decide which part your process to tackle first. You can then use some lean or six sigma tools release capacity.

Inventory is what we use to cope with less than perfect processes as it hides issues such as delays, poor quality, process time variations, supply shortages etc. Lean and six sigma will tend to push to reduce all inventory, while TOC will accept that some inventory is of value as a buffer. This is especially true for jobbing shops, where day to day balancing of work is difficult.