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Why Is Variation Considered the Enemy of Quality in Six Sigma?
Prepare for your Six Sigma Green Belt exam by understanding why variation is the enemy of quality. Learn how process variation leads to defects, unpredictability, and lower customer satisfaction, and why reducing it is the central focus of the Six Sigma methodology.
Question
In Six Sigma, variation in a process is considered…
A. The enemy of quality and consistency
B. A sign of creativity
C. Unavoidable and irrelevant
D. Evidence of poor customer service
Answer
A. The enemy of quality and consistency
Explanation
Variation leads to defects and lower quality. This statement represents one of the most fundamental principles of the Six Sigma methodology: the reduction of variation is the key to improving quality.
Variation as the Source of Unpredictability and Defects
In any business process, variation refers to the natural differences that occur in the output of that process over time. While some level of variation is always present, Six Sigma views excessive variation as the primary source of poor quality. This is because high variation leads directly to unpredictability and defects.
- Unpredictability: When a process has high variation, its output is inconsistent. This means you cannot reliably predict whether the next unit produced or the next service delivered will meet customer expectations. For example, if a call center’s average hold time is two minutes, but individual hold times vary from 10 seconds to 10 minutes, customers experience an unpredictable and often frustrating service. A process with low variation, however, is stable and predictable, consistently delivering results close to the target.
- Defects: A defect is defined as any output that falls outside of the customer’s specification limits. The more a process varies, the higher the probability that some of its output will breach these upper and lower limits, resulting in a defect. By systematically reducing variation, Six Sigma seeks to center the process around the target and narrow its spread so that virtually all output falls safely within the specification limits. This is how Six Sigma achieves its goal of 3.4 Defects Per Million Opportunities (DPMO).
Analysis of Incorrect Options
B. A sign of creativity: This is incorrect in the context of an operational process. While creativity is essential for innovation and design, the goal of an established process is consistent, repeatable execution. In this setting, “creativity” often means deviation from the standard procedure, which introduces variation and is a source of errors.
C. Unavoidable and irrelevant: This is false. While it’s true that some variation is unavoidable (known as common cause variation), it is never irrelevant. The entire purpose of Six Sigma is to identify, understand, quantify, and reduce all sources of variation as much as possible. To consider it irrelevant is to misunderstand the core of the methodology.
D. Evidence of poor customer service: This confuses cause and effect. High variation in a process is a cause of problems that can lead to poor customer service (e.g., late deliveries, inconsistent product quality). However, variation itself is a statistical property of a process, not direct evidence of the customer’s experience. Poor customer service is an outcome of a high-variation process.
Six Sigma Green Belt: Apply, Analyze & Improve certification exam assessment practice question and answer (Q&A) dump including multiple choice questions (MCQ) and objective type questions, with detail explanation and reference available free, helpful to pass the Six Sigma Green Belt: Apply, Analyze & Improve exam and earn Six Sigma Green Belt: Apply, Analyze & Improve certificate.