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Statistical Process Control Flashcards

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

Read the first 7 Statistical Process Control flashcards as text

  1. A hospital tracks the proportion of patients with surgical site infections each month with varying patient counts. Which chart is appropriate?

    Answer: p-chart

    The p-chart is designed for proportion of defective items (or events) when the sample size varies from period to period.

  2. The concept of 'rational subgrouping' in SPC means:

    Answer: Grouping samples so within-subgroup variation reflects only common causes

    Rational subgrouping ensures that units within a subgroup were produced under the same conditions, so between-subgroup differences reveal special causes.

  3. Which of the following is a key difference between Cp and Pp?

    Answer: Cp uses estimated sigma from the process; Pp uses actual standard deviation of all data

    Cp uses within-subgroup sigma estimated from R-bar/d2 (short-term), while Pp uses the overall standard deviation of all data (long-term), capturing more sources of variation.

  4. A process improvement team reduces the standard deviation of a process from 4 to 2 units without changing the mean. What happens to Cpk?

    Answer: Cpk doubles because the process spread is halved

    Cpk is inversely proportional to sigma; halving the standard deviation doubles Cpk, reflecting a more capable process.

  5. On a control chart, a 'trend' pattern (six or more consecutive points steadily increasing or decreasing) typically signals:

    Answer: A progressive special cause such as tool wear or gradual drift

    A sustained monotonic trend indicates a progressive special cause, such as tool wear, temperature buildup, or material depletion, driving a gradual process shift.

  6. What is the relationship between the control limits on a control chart and product specification limits?

    Answer: Control limits and specification limits are independent and serve different purposes

    Control limits are derived from process data and indicate process stability, while specification limits are customer-defined requirements — they are mathematically and conceptually independent.

  7. In SPC, 'tampering' refers to:

    Answer: Making process adjustments in response to common cause variation

    Tampering means reacting to individual data points that are within control limits (common causes) by adjusting the process, which actually increases overall variation.