SPC Data Collection & Interpretation 5

Question 1

Which formula correctly calculates the mean (Xbar) of a subgroup with values 8, 10, 12, and 14?

Accepted Answer

(8+10+12+14) / 4 = 11

Answer

The subgroup mean is the arithmetic average: sum all values and divide by the count, giving (44)/4 = 11.

Question 2

A quality team notices that data from one shift consistently shows higher average values. This is BEST addressed by:

Accepted Answer

Stratifying data by shift and investigating the shift-specific cause

Answer

Stratifying by shift isolates the factor causing the difference, enabling root cause analysis and targeted corrective action.

Question 3

In SPC data collection, a sampling plan that selects every nth unit is called:

Accepted Answer

Systematic sampling

Answer

Systematic sampling selects units at a fixed interval (every nth unit), providing even coverage across production without full randomization.

Question 4

Which statistic measures the spread of individual measurements within a subgroup on an Xbar-R chart?

Accepted Answer

Range (R)

Answer

The range R = maximum minus minimum within a subgroup measures within-subgroup variation, which is plotted on the R chart.

Question 5

When a process is described as 'in statistical control,' it means:

Accepted Answer

Only common cause variation is present and the process is stable and predictable

Answer

Statistical control means the process exhibits only inherent (common cause) variation, making future output predictable within control limits.

(SPC) Statistical Process Control Certification Practice Test