Within the Six Sigma DMAIC improvement cycle, which phase is specifically designed to ensure that a solved problem does not reoccur and that the new processes continue to improve over time?

Introduction / Context:
DMAIC is a widely used structured problem solving method in Six Sigma and process improvement projects. It stands for Define, Measure, Analyze, Improve and Control. This question asks you to identify the phase that focuses on preventing the solved problem from recurring and on sustaining and further improving the new process performance over time.

Given Data / Assumptions:
- We are working within the DMAIC framework.- Earlier phases have already defined the problem, measured data, analyzed root causes and implemented improvements.- The remaining task is to maintain the gains, standardize the solution and watch for further opportunities.- Options given correspond to different phases or related terms.

Concept / Approach:
In DMAIC, each phase has a distinct purpose. Define clarifies the problem and goals. Measure collects relevant data. Analyze finds the root causes. Improve designs and implements solutions. Control establishes monitoring, standard operating procedures and response plans to ensure that the improvements are sustained and that the process does not slip back to its old performance. Therefore, the phase associated with preventing recurrence is Control.

Step-by-Step Solution:
Step 1: Recall the full form of DMAIC and the typical sequence of activities in each phase.Step 2: Recognise that the Improve phase is where new solutions or process changes are implemented.Step 3: Understand that after improvements, another phase is needed to create control plans, control charts, checklists and documentation.Step 4: Identify this last phase as Control, whose objective is to maintain gains, monitor key metrics and react quickly to deviations.Step 5: Match this understanding with the options and select Control as the correct answer.

Verification / Alternative check:
An alternative way to check is to remember the typical deliverables of the Control phase: updated process maps, standard operating procedures, training materials, control charts and a response plan. These deliverables are clearly aimed at sustaining performance and making sure the project results do not fade away. No other phase in DMAIC has this sustaining objective as its primary focus. This confirms that Control, not Design, Analyze or Improve, is the phase that prevents the problem from recurring.

Why Other Options Are Wrong:
Design: In some methodologies like DMADV, Design is a phase for designing new processes or products, but in DMAIC it is not a standard phase and does not describe ongoing control.Analyze: This phase is used to determine root causes using data analysis and statistical tools, not to maintain improvements.Improve: This phase focuses on testing and implementing solutions to remove root causes, but without the follow up controls the system may drift back.

Common Pitfalls:
Learners sometimes think that once the Improve phase is completed, the project is effectively over, forgetting that performance can slowly degrade. Another common mistake is to mix DMAIC with other acronyms like DMADV and assume that Design must be part of every improvement cycle. In exams, always tie the word control to ideas like monitoring, standardization and preventing backsliding, which are the hallmarks of the Control phase in process improvement projects.

Final Answer:
In the DMAIC cycle, the phase that ensures the problem does not reoccur and that improvements are sustained is the Control phase.