The Difference between Kaizen and Six Sigma


I’m sure that most readers have heard of Six Sigma and know that it is about improving processes in order to reduce defects and therefore improve quality.   Some who are familiar with Japanese companies like Toyota know about the concept of kaizen or “continuous improvement”, with the emphasis on improvement that takes smaller, incremental steps rather than giant leaps of innovation.

How are these two different?   Well, aside from their cultural origins, Six Sigma originating in the US and kaizen originating in Japan, they both have two features in common.   Yes, they both operate on processes and they work on improvement of those processes to reach increasing higher standards.

But Six Sigma uses a rigorous statistical methodology for one, and it also emphasizes that the improvement of processes done under Six Sigma must be owned by those who carry out those processes.    The reason for this is that if a solution is reached and a process is improved, but the improvement is not owned by those who are doing the process, then they have no sense of responsibility to make sure that solution is maintained on a permanent basis.   This may be one of the explanations of something called the “1.5-Sigma Shift”, where a process that has been improved to a certain level of Sigma may, over the long run, have a certain amount of “slippage” or “regression” where the Sigma levels by about 1.5 Sigma on average.    If the solution is implemented on a temporary basis, but is not kept up, this could be one thing that accounts for the slippage in Sigma level over time.

The company Bombardier Aerospace Inc. has done internal studies that show that Kaizen initiatives may benefit a company initially, but only to about the 3 and 3.5 Sigma level.   To raise a company’s processes further, it requires more statistically rigorous techniques from Six Sigma to achieve 4 Sigma level or further.   It is when you get to the 5 Sigma level that it is not just the improvement of existing processes, but the creation or elimination of processes, particularly in the design phase, that take a company to the point of achieving quantum leaps of performance that take it beyond this stage, something that Kaizen alone is not equipped to deliver.

So rather than saying that Six Sigma is better than Kaizen, it is probably fairer to say that Kaizen is an attitude towards process improvement that can yield benefits to any company up to a certain point, but to improve beyond that point (in particular, beyond the 3 to 3.5-Sigma level) it is necessary to add a statistical rigor into process improvement that of the two, only Six Sigma can deliver.

The next post deals with how the methodology of Six Sigma and the science of statistics are inseparable.

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