Statistical Thinking and Variation Flashcards
7 cards from real Lean Six Sigma Yellow Belt Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Statistical Thinking and Variation flashcards as text
Control charts have control limits set at ±3 standard deviations from the mean because:
Answer: This range captures approximately 99.73% of common cause variation
Setting control limits at ±3 standard deviations captures 99.73% of natural process variation, making points outside the limits a strong signal of special causes.
What is the key difference between control limits and specification limits?
Answer: Control limits are calculated from process data; specification limits are set by customer requirements
Control limits reflect what the process actually does (derived from data), while specification limits reflect what the customer requires — they measure entirely different things.
A point falling outside the control limits on a control chart most likely indicates:
Answer: A special cause of variation has occurred
A point outside the control limits is a statistical signal that something unusual — a special (assignable) cause — has likely affected the process.
A histogram is used in Six Sigma primarily to:
Answer: Display the frequency distribution of process data
A histogram displays how often values fall within defined intervals, revealing the distribution shape, central tendency, and spread of process data.
What does a run chart help a Yellow Belt team identify?
Answer: Trends, shifts, or patterns in process data over time
A run chart plots data sequentially over time, helping teams detect non-random patterns such as trends, shifts, or cycles that may indicate special causes.
If a control chart shows a consistent upward trend of seven consecutive points, this is:
Answer: A signal of a special cause that should be investigated
Seven or more consecutive points trending in one direction is a recognized rule signaling special cause variation, even if none fall outside the control limits.
The Voice of the Process (VOP) represents:
Answer: What the process is actually capable of delivering based on its own performance data
VOP describes a process's actual capability and behavior as revealed by data, in contrast to VOC (Voice of the Customer) which represents external requirements.