## Re: Measurement system nalysis - Bias and linearity

Occasional Contributor

Joined:

Apr 18, 2017

In Our MSA stsudy we are performing Linearity and Bias measurment. We are currently controlling at Linearity and Bias to be below 5%.  We actually generate the following report for Linearity and BIas. However in AIAG handbook the criteria for the gauge to pass bias criteria has the following criteria in the picture attahcment

I have the following questions

1. We have set the linearity and Bias guidelines as less than 5%, however no one can identify how we derive the 5% criteria. Any guidelines on explanation why its 5%?

2. In the linearity and bias script there is dialog box where we enter a process sigma value- what should be this value? We are currently keying in the tolerance (USL-LSL) is this correct?(See powerpoint slides)

3. In the powerpoint slide case1  and case 2 - Case 2 the zero and bias lines are not within the confidence interval but its meeting the Bias% and Linearity% of less than 5% is this correct and accepatable?

3 REPLIES

Community Trekker

Joined:

Nov 17, 2014

Joanne Wendelberger's article about measure uncertainty in her article "Uncertainty in Designed Experiments" , Quality Engineering (2010), Vol 22: 88-100,  where she gave some historical context and formula derivations. Another source is W.J. Youden's Experimentation and Measurement, (1997, originally published in 1962), NIST Special Publication 672, U.S. Department of Commerce.

Staff

Joined:

Jun 16, 2014

For item two - the value you should enter in the dialog should not be the tolerance or spec limits. It should be a historical process standard deviation - perhaps from a control chart on the process. This number will be used in the calculations of the figures of merit.

For item 3 - Case number 1 the bias slope is not significant, so you can say there is no bias. For Case 2 - the slope of the line is significant - but it is is also not recognizing the non linearity in the data. The first 2 standards at 5 and 10 are close to 0 bias, but the third standard at 25 is high, and the last standard at 100 is low. This line is not a good fit to this data - there is a quadratic effect.

Case 1 looks okay - case 2 not so much.

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Occasional Contributor

Joined:

Apr 18, 2017

Thank you very much