The fourth level focuses on reducing variation in a stable process that is created in the first three levels. The objective is to increase predictability, quality and customer satisfaction. The improvement method used in this level is Six Sigma. This is a long-term strategy to improve performance by reducing variation.
At this stage statistical tools will be applied by Black Belts to analyze the performance of processes and products. Some of the tools are also applied by Yellow, Orange and Green Belts. In order to apply statistics, data is needed. Therefore at this stage it is important to have a performance measurement system in place that is able to deliver data of the process performance and at the level of the products that are produced.
Besides statistical tools Six Sigma also offers a structured approach for executing an improvement project. This approach is called the DMAIC roadmap which stand for Define – Measure – Analyze – Improve – Control. Although the DMAIC roadmap finds its origin in Six Sigma, it can be applied to Lean projects as well. The approach is too complex though for smaller projects like Kaizen initiatives. For these type of projects it is recommend to follow the PDCA roadmap.
Rather than increasing quality with a step-by-step approach like Kaizen proclaims, Six Sigma focuses on quality breakthrough improvement projects. An improvement project will take a few weeks or a few months rather than a few days. As a consequence the Six Sigma approach is much more top-down driven by Green and Black Belts, than the Kaizen bottom-up approach.