Control Phase in DMAIC: Sustaining Gains and Locking in Improvements

You've defined the problem. Measured the process. Analyzed root causes. Improved the performance. Now what?

Welcome to the Control Phase—the final step in the DMAIC (Define–Measure–Analyze–Improve–Control) cycle. Often underestimated, this phase is where the real test begins: can your team sustain the improvements over time?

In this post, we'll explore how to effectively execute the Control phase, what tools to use, and how to keep your hard-earned results from slipping back into old habits.

Why the Control Phase Matters

Think of the Control phase as installing a seatbelt for your process improvements. Without it, even the best solution can deteriorate over time due to:

• Staff turnover

• Poor communication of new procedures

• Lack of ongoing monitoring

• Incomplete training

• Confusion about who owns the process

Neglecting the Control phase is like remodeling your kitchen and never checking for leaks—eventually, things fall apart.

Objectives of the Control Phase

1. Sustain process gains

2. Maintain performance levels

3. Transfer ownership to the process team

4. Document and standardize changes

5. Set up response plans if performance dips

Key Tools and Techniques in the Control Phase

Let’s explore some of the most important tools that help “lock in” improvements:

1. Control Charts

Control charts monitor process variation over time. They help ensure the improved process is stable and performing within expected limits.

Example: A logistics company reduced order-to-shipment cycle time. A control chart for “hours per order” is created to monitor whether the cycle time stays within ±3 standard deviations.

• If the process strays outside the control limits or trends up/down, it signals a need to investigate.

• Common types: X-bar & R chart, Individuals (I-MR) chart, P chart for proportions.

2. Process Control Plan

A Control Plan summarizes:

• Critical process steps

• Key inputs and outputs

• Control methods

• Measurement frequency

• Reaction plans for when things go wrong

This becomes the go-to document for operators and supervisors to keep the process in check.

Tip: Make the plan a living document, not just a binder on a shelf.

3. Standard Operating Procedures (SOPs)

SOPs formalize the new process so it’s followed consistently by everyone—even if there’s turnover or shift changes.

Good SOPs include:

• Step-by-step tasks

• Roles and responsibilities

• Visual job aids or checklists

• Version control

A clear SOP is critical when improvements involve human-dependent activities (e.g., manual checks, email approvals, etc.).

4. Mistake-Proofing (Poka-Yoke)

Mistake-proofing reduces the opportunity for error. It can be as simple as redesigning a form to only accept numeric entries, or using a barcoding system to prevent the wrong label from being printed.

Examples:

• Color-coded trays for different test types in a lab

• E-commerce checkout systems that disable the “Submit” button unless all fields are completed

5. Training and Handover

Teams need proper training on the improved process, supported by checklists, shadowing, and knowledge transfer.

Plan for:

• Refresher training

• Onboarding of new staff

• Feedback collection from frontline workers

Training closes the loop between improvement and execution.

6. Response Plans and Escalation Matrix

What happens if the process starts drifting or breaks down? Build an early warning system with clear triggers and escalation steps.

A simple escalation matrix includes:

• What to monitor (e.g., defect rate >2%)

• Who reviews it (e.g., team lead, supervisor)

• What action to take (e.g., revert to last known good condition, trigger root cause review)

7. Audit Checklists

Periodic audits reinforce the new way of working. They help identify where old habits may be creeping back in and whether the SOPs and control plans are being followed.

Use simple checklists that ask:

• Is the process being followed as designed?

• Are control charts up to date?

• Are staff trained and certified?

Don’t aim for perfection—aim for awareness and accountability.

Transferring Ownership

A key success factor in the Control phase is handing over the process to the business. The improvement team or Six Sigma Belt should not remain the “owner.”

Steps for a clean handoff:

• Conduct a final walkthrough with process owners

• Review control plans, SOPs, and training records

• Assign a process owner who is accountable going forward

• Ensure KPIs are integrated into daily performance reviews

Real-World Example: Claims Processing Team

A health insurance company improved its claims processing time by eliminating rework and automating document verification. During the Control phase:

• A dashboard tracked average processing time daily

• Supervisors reviewed control charts weekly

• SOPs were updated and embedded in the onboarding system

• A monthly audit sampled 20 claims for compliance

• Agents were retrained on updated procedures

Six months post-project, the process remained stable and customer satisfaction had improved by 15%.

Wrapping Up: Think Sustainably

In Lean Six Sigma, improvement is not a one-time event—it’s a new way of working. The Control phase is your bridge from project to permanence.

If you skip this step, even the best-designed improvements will eventually unravel.

But if done right, Control transforms “project success” into process excellence—anchored in accountability, discipline, and data.