In this step, most critical causing the problem under study is isolated. Number of these causes is usually 2 to 3. Depending upon the need and complexity of the problem, various tools like Pareto chart, Fish bone diagram, 5 why analysis, regression analysis, histograms etc. can be used in this phase (DMAIC tools, n.d).
This step involves implementing a new improved system that avoids the problems identified in the above steps. Before fully implementing the improve process, a test process is executed in the short term to check its applicability and any possible hindrances in the organization. Some common tools used in this stage includes: regression, hypothesis testing, designed experiments, analysis of variance (ANOVA), and simulation (DMAIC tools, n.d).
Control phase involves “controlling the “vital few” variables, typically the top two or three, that we identified in the Analyze and Improve phases of the project” (DMAIC tools, n.d). There are certain control processes that do not require continuous monitoring. However, some of the improved processes require six sigma team keep a check on the new system to avoid any errors and defects. For this the team must performing constant error proofing to make the process viable and error free in the long run. (DMAIC tools, n.d).