Reproducibility

The variation contributed by Reproducibility; also known as Appraiser Variation. It is "corrected" to remove the effects of Repeatability error:

When the Number of Appraisers = 10:

When the Number of Appraisers > 10:

where:

EV is the Equipment Variation, or Repeatability

Ordinate is the specified Sigma Level (usually 2.575 for Gage R&R analysis)

d2* is based on m= the number of Appraisers and g = 1 subgroups.

C4 is based on m= the number of Appraisers and g = 1 subgroups

X-barDIFF is the range between the average measurements of the selected Appraisers (for all trials and all selected parts)

X-barSTDDEV is the standard deviation of the average measurements of the selected Appraisers (for all trials and all selected parts)

Notes:

1. Some authors, including AIAG, refer to the quantity (2*Ordinate/ d2*) as K2.

2. Table for d2* values may be found in A.J. Duncan, Quality Control and Industrial Statistics, 1965, Third Edition Richard D. Irwin, Homewood, Illinois. Table D3, pg. 910.

3. The Reproducibility Standard Deviation is simply AV/(2*Ordinate)

% AV is calculated using the Total Variation (TV):

% AV may also be calculated using the Part Tolerance:

where USL is the Upper Specification Limit and LSL is the Lower Specification Limit

Learn more about the Quality Improvement principles and tools for process excellence in Six Sigma Demystified (2011, McGraw-Hill) by Paul Keller, or his online Green Belt certification course ($499).