SPC Measurement System Analysis (MSA) 2 — Questions and Answers
Question 1: In a 'crossed' Gauge R&R study design, what is the key characteristic?
- Each operator measures only one unique set of parts
- Every operator measures every part multiple times (Correct answer)
- Parts are nested within operators so each operator measures different parts
- Only one operator measures all parts
Correct answer: Every operator measures every part multiple times
In a crossed design, every operator measures every part multiple times, allowing both repeatability and reproducibility to be fully estimated and separated.
Question 2: When is a 'nested' Gauge R&R design typically used instead of a crossed design?
- When the measurement process is destructive and parts cannot be re-measured (Correct answer)
- When there are more than five operators in the study
- When the gauge is automated and requires no operator
- When all parts come from the same production lot
Correct answer: When the measurement process is destructive and parts cannot be re-measured
Nested (or hierarchical) designs are used for destructive testing where each part can only be measured once, preventing the crossed design's repeated measurements.
Question 3: In a Gauge R&R ANOVA output, what does '%Contribution' represent?
- The percentage of parts that are out of tolerance
- The percentage of total observed variation attributable to each source (gauge, operators, parts) (Correct answer)
- The percentage of the specification tolerance consumed by the gauge
- The percentage of operators who passed the study
Correct answer: The percentage of total observed variation attributable to each source (gauge, operators, parts)
%Contribution shows the proportion of total variance in the study that is attributable to each variation source such as repeatability, reproducibility, and part-to-part variation.
Question 4: What is the 'Number of Distinct Categories' (ndc) metric used for in a Gauge R&R study?
- To count how many different gauges were used in the study
- To indicate how many statistically distinct groups the measurement system can differentiate within the process variation (Correct answer)
- To determine the number of operators needed for a valid study
- To count the number of defect categories the gauge can detect
Correct answer: To indicate how many statistically distinct groups the measurement system can differentiate within the process variation
The ndc indicates the number of non-overlapping confidence intervals that can span the range of product variation, showing the measurement system's ability to distinguish between parts; a value of 5 or more is generally desired.
Question 5: What advantage does the ANOVA method provide over the Average and Range (X-bar & R) method in Gauge R&R analysis?
- It requires fewer parts and operators to run
- It can separate the operator-by-part interaction as a distinct source of variation (Correct answer)
- It automatically calibrates the measurement instrument
- It eliminates the need for a reference standard
Correct answer: It can separate the operator-by-part interaction as a distinct source of variation
ANOVA can identify and quantify an operator-by-part interaction effect, which the Average and Range method cannot detect, providing a more complete picture of variation sources.
Question 6: Attribute Agreement Analysis (AAA) is used when the measurement outcome is:
- A continuous variable measured on a calibrated scale
- A pass/fail or categorical classification rather than a numeric value (Correct answer)
- A value derived from a regression equation
- A ratio of two continuous measurements
Correct answer: A pass/fail or categorical classification rather than a numeric value
Attribute Agreement Analysis evaluates measurement systems that produce categorical (pass/fail, good/bad, grade A/B/C) outcomes rather than continuous numeric measurements.
Question 7: In Attribute Agreement Analysis, 'Kappa' statistic values close to 1.0 indicate:
- Poor agreement between appraisers beyond chance
- Strong agreement between appraisers beyond what would be expected by chance (Correct answer)
- The measurement system is biased toward accepting bad parts
- The number of parts inspected is insufficient
Correct answer: Strong agreement between appraisers beyond what would be expected by chance
Kappa measures agreement between appraisers (or against a reference standard) corrected for chance agreement; values near 1.0 indicate near-perfect agreement, while values near 0 indicate agreement no better than chance.
SPC Measurement System Analysis (MSA) 2
In a 'crossed' Gauge R&R study design, what is the key characteristic?