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.
Read the first 7 Statistical Process Control flashcards as text
When plotting an Individuals (I) chart, the moving range is typically calculated using how many consecutive observations?
Answer: 2 consecutive points
The moving range in an I-MR chart uses successive pairs of two consecutive observations to estimate short-term process variation.
A CPHQ exam scenario describes a Sigma level of 4.0 for a medication dispensing process. Approximately what percentage of outputs fall outside specification limits?
Answer: 0.62%
A 4-sigma process has approximately 0.62% of outputs outside specification limits (6,210 DPMO), reflecting high but not Six Sigma quality.
A quality team observes that all 15 consecutive points on a control chart fall within the 1σ zone of the centerline. Which pattern does this represent?
Answer: Stratification, suggesting data from multiple process streams is mixed
Fifteen consecutive points within 1σ (Western Electric Rule 5) suggests stratification—data is likely sampled from different sub-populations with different means.
For the CPHQ exam, which measure is used as the centerline of an R chart?
Answer: Average of subgroup ranges (R-bar)
The centerline of an R chart is R-bar, the average of the subgroup ranges collected during the baseline period.
A healthcare quality director wants to assess long-term process performance. Which capability metric should she use?
Answer: Pp, based on total observed variation
Pp (and Ppk) use total process variation (overall standard deviation), reflecting long-term performance, while Cp/Cpk use short-term within-subgroup variation.
Which of the following is a correct interpretation of an out-of-control signal on a control chart?
Answer: A special cause of variation is likely present and should be investigated
An out-of-control signal means a special cause is likely present, triggering investigation—it does not necessarily mean defects are being produced.
In rational subgrouping for an SPC chart in a hospital laboratory, samples should be grouped to:
Answer: Minimize variation within subgroups and allow between-subgroup variation to represent process changes
Rational subgrouping minimizes within-subgroup variation (produced under similar conditions) so that between-subgroup differences reveal true process changes.