The Control Phase represents the final and arguably most critical stage of the DMAIC (Define, Measure, Analyze, Improve, Control) methodology in Lean Six Sigma. Many practitioners struggle with determining when they have truly completed this phase and can confidently close out their project. Understanding the exit criteria for the Control Phase ensures that improvements remain sustainable and that your organization reaps long-term benefits from the investment made in process improvement initiatives.
This comprehensive guide will walk you through the essential elements of Control Phase completion, providing you with a detailed checklist, real-world examples, and practical insights to determine when your Six Sigma project is ready for handoff to process owners. You might also enjoy reading about Benefits Realization Tracking: Proving ROI After Project Completion.
Understanding the Significance of the Control Phase
Before diving into exit criteria, it is essential to understand why the Control Phase holds such importance in the Six Sigma methodology. After spending considerable time and resources defining problems, measuring current performance, analyzing root causes, and implementing improvements, the Control Phase acts as the guardian ensuring that gains are maintained over time. You might also enjoy reading about Process Monitoring Frequency: How Often Should You Check Your Metrics for Optimal Performance.
Studies show that approximately 70% of process improvements fail to sustain their results beyond the first year when proper controls are not established. This statistic underscores the critical nature of completing the Control Phase thoroughly rather than rushing to close out projects prematurely. You might also enjoy reading about Early Warning Systems: Detecting Problems Before They Become Defects.
The Control Phase serves multiple purposes within the organization. It establishes monitoring systems, creates response plans for deviations, transfers ownership to process stakeholders, and documents lessons learned for future initiatives. Without proper completion of this phase, organizations risk reverting to old processes and losing all the hard-won improvements achieved during the project.
The Comprehensive Exit Criteria Checklist
Determining when the Control Phase is complete requires evaluation across several dimensions. The following checklist provides a structured approach to assess project readiness for closure.
1. Statistical Process Control Implementation
Statistical Process Control (SPC) charts must be established and operational for all critical process parameters. These charts serve as the early warning system that alerts process owners when the process begins to drift from its improved state.
Exit criteria requirements:
- Control charts are created for all key process output variables (KPOVs) and critical input variables (KPIVs)
- Control limits are calculated based on post-improvement data
- At least 25 to 30 data points are collected after improvements to establish reliable control limits
- The process demonstrates statistical stability with no special cause variation
- Process capability indices (Cpk) meet or exceed target values (typically 1.33 or higher)
Example with sample data:
Consider a manufacturing process improvement project focused on reducing defect rates in electronic component assembly. During the Improve Phase, the team implemented new quality inspection procedures and operator training programs. To verify Control Phase readiness, they collected defect rate data over six weeks post-implementation.
The sample data showed the following weekly defect rates (defects per million opportunities):
- Week 1: 3,200 DPMO
- Week 2: 3,100 DPMO
- Week 3: 3,400 DPMO
- Week 4: 2,900 DPMO
- Week 5: 3,300 DPMO
- Week 6: 3,000 DPMO
The team calculated an average defect rate of 3,150 DPMO with control limits of 2,600 to 3,700 DPMO. All data points fell within control limits, indicating statistical stability. The process capability analysis revealed a Cpk of 1.45, exceeding the minimum requirement of 1.33. This statistical evidence supported the completion of this exit criterion.
2. Documentation and Standard Operating Procedures
Comprehensive documentation ensures that knowledge about the improved process is preserved and accessible to all relevant stakeholders. This documentation becomes the foundation for training and serves as a reference point for future process audits.
Exit criteria requirements:
- Updated standard operating procedures (SOPs) reflect all process changes
- Work instructions are revised and include visual aids where appropriate
- Process maps accurately depict the current state workflow
- Control plans document monitoring frequency, measurement methods, and response procedures
- All documents are reviewed, approved, and uploaded to the document management system
- Version control is established to track future revisions
Practical example:
In a customer service improvement project at a telecommunications company, the team reduced average call handling time from 12.5 minutes to 8.2 minutes while maintaining customer satisfaction scores. Before declaring the Control Phase complete, they updated 15 separate documents including call scripts, escalation procedures, and troubleshooting guides.
Each document underwent a three-level review process involving subject matter experts, quality assurance personnel, and department managers. The updated SOPs included screenshots of the new customer relationship management system interface and flowcharts depicting decision trees for common customer issues. These documents were then uploaded to the company intranet with restricted edit access to maintain integrity.
3. Training and Knowledge Transfer
Process improvements can only be sustained when the people operating the process understand what has changed, why it changed, and how to maintain the new methods. Effective knowledge transfer is non-negotiable for Control Phase completion.
Exit criteria requirements:
- Training materials are developed covering all process changes
- All affected personnel have completed training sessions
- Training effectiveness is assessed through testing or practical demonstration
- Training records are documented and filed appropriately
- Refresher training schedule is established for new hires and existing staff
- Subject matter experts are identified who can provide ongoing support
Real-world application:
A hospital implemented improvements to its patient discharge process, reducing average discharge time from 4.5 hours to 2.1 hours after physician discharge orders were written. The project team developed a comprehensive training program that included classroom instruction, hands-on simulation, and shadowing experienced staff members.
Training was rolled out to 87 nurses, 23 case managers, and 12 administrative staff members over a three-week period. Each participant completed a post-training assessment, with a passing score set at 85%. Initial pass rates were 78%, prompting the team to provide additional training to 19 individuals who scored below the threshold. Once all personnel demonstrated competency, this exit criterion was satisfied. The hospital also scheduled quarterly refresher training and made training mandatory for all new hires during onboarding.
4. Response Plans and Escalation Procedures
Even well-controlled processes occasionally experience deviations. Having predetermined response plans ensures rapid correction when issues arise, preventing small problems from becoming major setbacks.
Exit criteria requirements:
- Response plans are documented for each monitored metric
- Threshold values trigger investigation and corrective action
- Escalation procedures identify who must be notified at each severity level
- Corrective action timeframes are specified
- Roles and responsibilities for investigation and resolution are clearly defined
- Response plans have been tested through simulation or actual application
Sample scenario:
A food processing company improved its packaging line efficiency from 68% Overall Equipment Effectiveness (OEE) to 89% OEE. As part of their Control Phase, they established a tiered response plan for OEE performance:
Level 1 (OEE drops to 85-87%): Line operator investigates and documents cause within 30 minutes. Shift supervisor is notified.
Level 2 (OEE drops to 80-84%): Production supervisor initiates formal investigation. Maintenance team inspects equipment. Report filed within 2 hours.
Level 3 (OEE drops below 80%): Plant manager notified immediately. Cross-functional team assembled. Production may be halted for detailed analysis. Root cause analysis completed within 24 hours.
The team tested this response plan during the final weeks of the Control Phase when OEE temporarily dropped to 83% due to a pneumatic valve issue. The response plan was activated successfully, with the problem identified and resolved within 90 minutes, validating the effectiveness of the established procedures.
5. Process Owner Acceptance and Transition
The ultimate goal of any Six Sigma project is to hand off a sustainable, improved process to the individuals responsible for its daily operation. Process owner acceptance signifies their readiness and willingness to maintain the improvements.
Exit criteria requirements:
- Process owner has been actively involved throughout the Control Phase
- Formal transition meeting has been conducted
- Process owner demonstrates understanding of control mechanisms
- Process owner accepts responsibility for ongoing monitoring
- Written sign-off is obtained acknowledging the transfer
- Support resources and escalation contacts are provided to process owner
Implementation example:
An insurance claims processing improvement project reduced average claim processing time from 14 days to 6 days. During the transition phase, the project Black Belt met with the Claims Department Manager on five separate occasions to review control charts, demonstrate the monitoring dashboard, and practice responding to simulated process deviations.
The Claims Department Manager participated in a formal acceptance meeting attended by the project sponsor, Black Belt, and key stakeholders. During this meeting, the manager demonstrated competency by explaining the control plan, identifying which metrics indicated process health, and describing appropriate responses to various scenarios. The manager then signed a Process Ownership Transfer Document, officially accepting responsibility for maintaining the improved process. A 90-day post-transition review was scheduled to ensure continued success.
6. Sustained Performance Verification
Brief success does not guarantee long-term sustainability. Verifying that improvements have held steady over a reasonable period provides confidence that controls are effective.
Exit criteria requirements:
- Improved performance is sustained for a minimum period (typically 4-8 weeks)
- Performance remains within control limits during this period
- Process capability continues to meet target values
- No major special causes have occurred
- Financial benefits continue to accrue as projected
Data-driven example:
A logistics company improved its on-time delivery rate from 82% to 96% through route optimization and driver scheduling improvements. To verify sustained performance, they tracked delivery performance for eight weeks following full implementation:
- Week 1: 95.8% on-time
- Week 2: 96.2% on-time
- Week 3: 95.5% on-time
- Week 4: 96.7% on-time
- Week 5: 96.1% on-time
- Week 6: 95.9% on-time
- Week 7: 96.4% on-time
- Week 8: 96.3% on-time
The average performance of 96.1% exceeded the target of 96% with a standard deviation of 0.36%. This consistent performance over the eight-week verification period provided strong evidence that improvements were sustainable and that this exit criterion was satisfied.
7. Financial Benefits Validation
Most Six Sigma projects are justified based on projected financial returns. Validating that actual benefits match or exceed projections is essential for project closure.
Exit criteria requirements:
- Financial impact is calculated using actual post-improvement data
- Calculations are verified by finance department or controllers
- Cost savings or revenue increases meet or exceed projections
- Benefit tracking mechanism is established for ongoing monitoring
- Any implementation costs are accurately documented
- Return on investment (ROI) is calculated and documented
Financial example:
A manufacturing plant project aimed to reduce raw material waste in a chemical mixing process. Initial projections estimated annual savings of $180,000 based on reducing waste from 8.5% to 3.5% of raw material input.
After three months of controlled operation, actual waste rates averaged 3.2%, slightly better than the target. The finance department calculated actual savings based on three months of data:
Monthly raw material cost: $450,000
Previous waste rate: 8.5% = $38,250 monthly waste cost
Current waste rate: 3.2% = $14,400 monthly waste cost
Monthly savings: $23,850
Annualized savings: $286,200
The project implementation costs totaled $45,000 (employee time, consultant fees, equipment modifications). The annualized ROI calculation showed:
ROI = (Annual Savings – Implementation Costs) / Implementation Costs x 100
ROI = ($286,200 – $45,000) / $45,000 x 100 = 536%
The finance department verified these calculations and signed off on the financial benefits, satisfying this exit criterion and exceeding original projections by 59%.
8. Dashboard and Reporting Systems
Sustainable improvements require ongoing visibility. Establishing effective reporting systems ensures that process performance remains transparent and that degradation is quickly identified.
Exit criteria requirements:
- Automated or semi-automated dashboard is operational
- Dashboard displays all critical metrics with visual indicators
- Reporting frequency is established and appropriate for process nature
- Access permissions are configured for relevant stakeholders
- Dashboard maintenance responsibilities are assigned
- Exception reporting triggers are configured
Practical implementation:
A retail company improved its inventory accuracy from 87% to 97.5% across 45 store locations. The project team developed a web-based dashboard displaying real-time inventory accuracy metrics for each location, with color coding to indicate performance status (green for 96% or above, yellow for 93-95.9%, red for below 93%).
The dashboard updated daily at 6:00 AM with the previous day’s cycle count results. Regional managers received automated email alerts whenever a store dropped into yellow or red status. The dashboard also displayed trend charts showing four-week rolling averages and highlighted any locations showing declining trends even if still within acceptable ranges. The IT department assumed responsibility for dashboard maintenance, with the inventory control manager serving as the primary user administrator.
Common Pitfalls to Avoid
Understanding what can go wrong during Control Phase completion helps teams avoid common mistakes that jeopardize sustainability.
Premature Project Closure
The pressure to demonstrate results and move on to new projects often leads teams to close projects before controls are truly established. Resist the temptation to declare victory after just one or two weeks of improved performance. Sustainable change requires patience and verification over an adequate time period.
Inadequate Process Owner Preparation
Handing off controls to process owners who lack understanding or commitment sets projects up for failure. Invest sufficient time in building process owner capability and ensuring their genuine buy-in before transitioning responsibility.
Overcomplicated Control Systems
Some teams create elaborate control mechanisms that are impractical to maintain in daily operations. The best control systems balance rigor with simplicity, making it easy for operators to comply without excessive burden.
Missing Documentation
Incomplete or unclear documentation creates confusion and increases the likelihood of process drift. Every change must be thoroughly documented, reviewed, and made accessible to relevant personnel.
The Role of Leadership in Control Phase Success
Leadership
