Perhaps the most critical aspect of Control is establishing a plan to monitor the new process and act when results are not up to spec, so that the project gains will be maintained. It is this component of Six Sigma projects that tends to distinguish them from basic project management methodology, whereby the project is closed out once the improvement is confirmed. The monitoring plan clarifies how the process performance will be continuously monitored, who will be notified if there is a problem and how that will happen and what response is required.
The first part of the monitoring plan specifies the metrics that will be tracked to summarize process performance, as well as specifying how and how often they will be tracked. Also be sure to clarify who is responsible for doing it; usually it falls to the process owner. Typically the metrics used during Measure and Improve and established as Critical To Quality (CTQ) measures during Define are appropriate.
The monitoring plan also indicates what constitutes satisfactory performance and what should be considered a red flag indicating possible problems. The team should brainstorm potential issues and appropriate responses for each. Again be sure to specify not only what needs to be done but who is responsible for making it happen.
A control chart should be continuously updated so that the process owner can watch for process shifts or other signs that there may be a problem with process performance. If the process owner is not well versed in interpreting control charts, the project team should create a reference sheet indicating what the process owner should be looking for. If possible, use an automated process to flag the process owner when performance becomes questionable.
Finally, since further change in the process environment is inevitable, the project team should develop a process for updating the new procedures when required. The update process will include updating the process map and user guides, communicating the changes to all involved, and modifying the monitoring plan if necessary to reflect the changes. Common changes that the team should plan for include shifts in employee roles, changes in customer specs and replacements for existing technology.