THE RASCH MODEL FOR TEST CONSTRUCTION AND PERSON MEASUREMENT
Measurement Systems Analysis€¦ · Reproducibility: Consistency of measurement results from...
Transcript of Measurement Systems Analysis€¦ · Reproducibility: Consistency of measurement results from...
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Chapter 2-5
Measurement Systems
Analysis
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ANALYZE
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MEASURE
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Less Sophisticated Measures?
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Measurement System Error
Data must be accurate.
All data have measurement errors.
Measurement errors come from primarily two sources:
Measurement equipment (Repeatability)
Measurement individual (Reproducibility)
Gage Repeatability and Reproducibility
(Gage R & R)
Can multiple data collectors using multiple measurement
equipment get the “same” results every time? And if not, is the
difference due to the equipment, the people, or error?
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Measurement Variation Control
Determine variation components.
1. Product variation
2. Equipment variation
3. Appraiser variation
Analyze results.
Specify corrective action.
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Precision vs Accuracy
Accuracy Problems – Not Centered on
Target
Calibration problem
Precision Problems – Too Much
Variation
Equipment Problem
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Accurate & Precise
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Accurate but not Precise
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Precise but Not Accurate
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Neither Accurate nor Precise
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Precision vs Accuracy
Gage R & R assumes that neither of the last 2 conditions exist in the system being studied (Precise but not accurate and Neither accurate nor precise).
That is, Gage R & R Assumes Gage is Calibrated
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Precision vs Accuracy
Precision components of Gage R & R:
Repeatability: Ability of the same measurement individual to get consistent measurements
Reproducibility: Consistency of measurement results from person to person when measuring the same part.
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General Suggestions for the Gage Study
Study involves using the gage to measure multiple parts by multiple appraisers in multiple randomized part sequence trials.
10 parts, 2 or 3 appraisers and two or three trials is considered optimal
Analysis of variance can be
performed. SPC XL uses
ANOVA
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Gage Study Example
Data collected for 5 gages (1,2,3,4,5) measured 3 times(Trial 1, Trial 2 and Trial 3) by two appraisers (A,B).
Trial 1 Sequence=4,5,2,1,3
Trial 2 Sequence=3,2,5,1,4
Trial 3 Sequence=1,4,3,2,5
Randomized
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Gage Study Data Example
Appraiser 1 Appraiser 2
Trial 1 Trial 2 Trial 3 Trial 1 Trial 2 Trial 3
Gage 1 0.34 0.42 0.38 0.28 0.32 0.24
Gage 2 0.50 0.56 0.48 0.54 0.48 0.44
Gage 3 0.42 0.46 0.40 0.38 0.42 0.34
Gage 4 0.44 0.48 0.38 0.46 0.44 0.40
Gage 5 0.26 0.30 0.28 0.30 0.28 0.36
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Use SPC XL, MSA (gage capability),
Create MSA Template
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Enter the Data in the SPC XL MSA Template
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Use SPC XL, MSA (gage capability), ANOVA Analysis on the completed MSA Template
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Completed ANOVA for MSA
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Explore Additional Analyses on the Excel
Tabs
MSA- Operator by Part
MSA- Sig Product by Sig Total
MSA- Measurement Pareto
MSA- Xbar Chart
MSA- Range Chart
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Homework Assignments
Project
Problem Set 2 on the class web
site
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