CPHQ Statistical Process Control 3

Question 1

Process capability index Cpk differs from Cp in that Cpk:

Accepted Answer

Accounts for process centering relative to specification limits

Answer

Cpk considers both spread and how well the process mean is centered within specifications, while Cp only measures spread relative to spec width.

Question 2

A healthcare quality team wants to determine if a patient wait-time process is stable before calculating capability. What must they confirm first?

Accepted Answer

The control chart shows the process is in statistical control

Answer

Process capability indices are only meaningful for stable (in-control) processes; an out-of-control process has unpredictable future performance.

Question 3

Which of the following best explains why using individual (I-MR) charts is appropriate for slow healthcare processes like monthly infection rates?

Accepted Answer

Subgrouping is impractical when data is collected infrequently

Answer

When data is collected too infrequently to form rational subgroups, I-MR charts are used with individual measurements.

Question 4

A control chart's UCL for an X-bar chart is calculated as X-double-bar + A₂R-bar. What does the constant A₂ depend on?

Accepted Answer

The subgroup size

Answer

The control chart constant A₂ is derived from the expected value of the relative range and varies with the subgroup sample size n.

Question 5

In SPC, a 'false alarm' (Type I error) occurs when:

Accepted Answer

The chart signals an out-of-control condition when the process is actually stable

Answer

A Type I error (false alarm) in SPC means the chart signals a special cause when in reality the process has not changed.

CPHQ - Certified Professional in Healthcare Quality Practice Test