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 Author Topic:   Acceptance Criteria for Linearity NeilLurker (<10 Posts) Posts: 5From:Welland, Ontario, CanadaRegistered: Mar 2001 posted 26 March 2001 03:27 PM                It is clear that the auditors are now expecting full MSA studies (i.e. bias, stability, linearity) not just Gauge R&R. What are you using for your acceptance criteria for linearity and why? Any insight would be appreciated.IP: Logged Atul KhandekarForum Contributor Posts: 21From:Pune, IndiaRegistered: Mar 2000 posted 27 March 2001 08:15 AM                I think 'Goodness of Fit' AND the 'Slope' of Regression Line are the factors to look at. If there is a uniform bias over the range of the instrument, the regression line will be horizontal and if G-of-F is low, the line has no meaning. However, I couldn't find any guidelines as to the actual value at which the G-of-F can be called 'low'.Again, the slope of the line may well be zero and Goodness of Fit > 0.9, but what value of bias should be accepted?Help!IP: Logged Al DyerForum Wizard Posts: 622From:Lapeer, MI USARegistered: Oct 2000 posted 10 April 2001 05:43 PM                Just from a practical point of view,As the result of a long term linearity study on a height gage, the following hypothetical results are realized.I base this on the simplified definition that linearity is the measurement of bias over the range of the gage.From 0 - 1" the bias is .0010From 1 - 2" the bias is .0015From 2 - 3" the bias is .0200From 3 - 4" the bias is .0200From 4 - 5" the bias is .0015From 5 - 6" the bias is .0010What is the acceptable criteria for linearity? I really don't know or care.My care:With the documented results I can determine which products/characteristics can be measured with the height gage.If my targeted dimension is .500 +/- .010 I "would" feel comfortable using the gage.If my targeted dimension is 2.500 +/- .010 I "would not" feel comportable using the gage.If my targeted dimension is 5.500 +/- .010 I "would" feel comportable using the gage.I don't know the correct term, is it the "10% discrimination rule" or the "10 to 1 rule"Am I making sense? Need help from the gurus!ASD...[This message has been edited by Al Dyer (edited 10 April 2001).]IP: Logged MSAFAIForum Contributor Posts: 24From:Tehran - IRANRegistered: May 2001 posted 13 May 2001 07:44 PM                Hi guys,someone with a PhD in statistics told me a goodness of fit of about 0.7 is sufficient.About the slope of the line, I have the same question: how much is acceptable?Or maybe the linearity analysis is used just to estimate the bias at vaious working values?Anyone can help?MSAFAIIP: Logged
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