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Statistical Process Control Flashcards

7 cards from real CPHQ practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  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?

    Answer: u-chart

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

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

    Answer: 0.27%

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

  3. When should a healthcare team recalculate control chart limits?

    Answer: After a confirmed, sustained process change or improvement

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

  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?

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

    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.

  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?

    Answer: Declare a special cause signal and investigate the improvement

    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.

  6. In SPC terminology, a process is said to be 'in statistical control' when:

    Answer: Only common cause variation is present and no control chart rules are violated

    Statistical control means the process exhibits only random (common cause) variation with no signals of special causes on the control chart.

  7. Which action is appropriate when special cause variation is identified on a healthcare control chart?

    Answer: Identify and eliminate the root cause of the special cause

    Special cause variation requires root cause analysis and elimination; attempting to adjust a process for special causes without investigation leads to over-control (tampering).