Practice Test Geeks(SPC) Statistical Process Control Certification Practice Test
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Control Charts & Analysis Flashcards

7 cards from real SPC 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 control chart with all points within control limits but 12 consecutive points on one side of the centerline is considered:

    Answer: Out of control due to a run rule violation

    Eight or more consecutive points on one side of the centerline violates the run rule, indicating a process shift even though no points exceed the ±3 sigma limits.

  2. Which statistic is used to estimate sigma (σ) from the average moving range on an I-MR chart?

    Answer: MR-bar / d2, where d2 = 1.128

    For an I-MR chart, the process standard deviation is estimated as MR-bar divided by d2, and for span-2 moving ranges d2 equals 1.128.

  3. Stratification on a control chart — where points cluster unusually close to the centerline — typically indicates:

    Answer: Data from multiple process streams mixed into one subgroup

    Stratification occurs when subgroups are formed by mixing data from multiple process streams, causing within-subgroup variation to artificially inflate the control limits.

  4. For a process with Cp = 1.33 and Cpk = 0.85, what can be concluded?

    Answer: The process has adequate spread but is off-center

    Cp > 1.33 indicates sufficient spread potential, but Cpk < 1.00 shows the process mean is not centered within the specification limits.

  5. Which control chart is best suited for monitoring a short-run production environment where part numbers change frequently?

    Answer: Standardized (Z) chart

    Standardized (Z) charts convert measurements to Z-scores relative to each part's target and tolerance, allowing multiple part types to be plotted on a single chart.

  6. The CUSUM chart is particularly sensitive to detecting:

    Answer: Small, sustained shifts in the process mean (0.5–1.5 sigma)

    CUSUM (Cumulative Sum) charts accumulate deviations from a target and excel at detecting small, persistent mean shifts that traditional Shewhart charts often miss.

  7. When should control limits be recalculated on an existing control chart?

    Answer: After confirmed special causes are identified, investigated, and corrected

    Control limits should be recalculated only after special causes are confirmed, root-caused, and permanently corrected to reflect the new stable process baseline.