FREE Lean Six Sigma Black Belt Control Phase: SPC Questions and Answers

Question 1

A quality team is monitoring the number of non-conforming units from a production line.
Due to fluctuating daily production schedules, the number of units inspected each day varies.
Which control chart is the most appropriate for monitoring the process performance under these conditions?

Accepted Answer

p-chart

Answer

np-chart

Answer

c-chart

Answer

u-chart

Question 2

An Xbar-R chart for a stable process shows eight consecutive points trending steadily downwards, although all points remain within the upper and lower control limits. According to the Western Electric rules for identifying special cause variation, what is the correct interpretation?

Accepted Answer

The process is exhibiting special cause variation and requires investigation.

Answer

Since no points are outside the control limits, the process is considered in control.

Answer

The control limits are too wide and should be recalculated immediately.

Answer

The process is showing natural, common cause variation and no action is needed.

Question 3

A process is being monitored with an Xbar chart and is determined to be in a state of statistical control. Despite this, a high percentage of the output is being rejected for failing to meet customer requirements. What is the most likely cause of this issue?

Accepted Answer

The control limits (voice of the process) are wider than the specification limits (voice of the customer).

Answer

The measurement system is flawed.

Answer

The process has too much special cause variation.

Answer

The specification limits are wider than the control limits.

Question 4

A Black Belt is establishing an Xbar-S chart to monitor the fill weight of a product. To ensure the chart is sensitive to shifts in the process average, data must be collected in rational subgroups. Which of the following data collection strategies best represents rational subgrouping?

Accepted Answer

Collecting 5-7 consecutive units at a specific point in time, with this sampling repeated periodically.

Answer

Collecting 50 consecutive units once at the end of each shift.

Answer

Mixing units from three different production lines to form one subgroup.

Answer

Collecting one unit every hour over an 8-hour shift to form a subgroup of 8.

Question 5

For a critical process characteristic, a team needs a control chart that is more sensitive to detecting small, sustained shifts in the process mean than a standard Shewhart chart (like an Xbar chart). Which of the following charts is specifically designed for this purpose?

Accepted Answer

CUSUM chart

Answer

p-chart

Answer

I-MR chart

Answer

Pareto chart

Question 6

Which of the following BEST describes the primary purpose of a Control Plan developed during the Control phase of a DMAIC project?

Accepted Answer

To provide a detailed, documented plan for monitoring process inputs and outputs to ensure that project gains are sustained.

Answer

To serve as the final project report summarizing the financial benefits and lessons learned for executive leadership.

Answer

To outline the statistical analysis and hypothesis tests that were performed in the Analyze phase.

Answer

To document the brainstorming and solution-selection activities from the Improve phase.

A quality team is monitoring the number of non-conforming units from a production line.Due to fluctuating daily production schedules, the number of units inspected each day varies.Which control chart is the most appropriate for monitoring the process performance under these conditions?

A quality team is monitoring the number of non-conforming units from a production line.
Due to fluctuating daily production schedules, the number of units inspected each day varies.
Which control chart is the most appropriate for monitoring the process performance under these conditions?