CPHQ Statistical Process Control 5

Question 1

A neonatal ICU tracks central-line-associated bloodstream infections (CLABSIs) per 1,000 line-days. The monthly line-days vary. Which chart is most appropriate?

Accepted Answer

u-chart

Answer

The u-chart is ideal for rare event counts (CLABSIs) per variable unit of exposure (line-days), adjusting control limits for varying denominators.

Question 2

A Shewhart control chart uses 3-sigma limits. What probability of a false alarm does this correspond to for normally distributed data?

Accepted Answer

0.27%

Answer

For normally distributed data, 99.73% of points fall within ±3σ, leaving a 0.27% false-alarm probability per point.

Question 3

When should a healthcare team recalculate control chart limits?

Accepted Answer

After a confirmed, sustained process change or improvement

Answer

Control limits should be recalculated when a verified, sustained process change has occurred—not in response to individual signals or routine schedules.

Question 4

A quality analyst is choosing between an X-bar & R chart and an X-bar & S chart for monitoring blood glucose turnaround times with subgroup size n=12. Which should she choose and why?

Accepted Answer

X-bar & S, because the S chart is more efficient for subgroup sizes larger than about 8–10

Answer

For subgroups larger than 8–10, the S chart (using standard deviation) is statistically more efficient than the R chart (using range) at detecting variability changes.

Question 5

A hospital's patient fall rate has been stable for 18 months. Administration mandates a new rounding protocol. After implementation, five consecutive months show rates below the previous centerline. What is the appropriate SPC action?

Accepted Answer

Declare a special cause signal and investigate the improvement

Answer

Five consecutive points below the centerline violate a run rule, signaling a special cause—in this case, likely a beneficial process change worth investigating and institutionalizing.

CPHQ - Certified Professional in Healthcare Quality Practice Test

CPHQ - Certified Professional in Healthcare Quality Practice Test

CPHQ Statistical Process Control 5