Unfortunately, the manual never comes out directly and states the acceptance criteria, but it does make a vague reference to GRR, so I think you are safe in making that assumption of 10% acceptance criteria.

Hi Miner, i would like to ask 2 questions related to Bias Study to you,..

I noticed that in most of the statistical softwares, be it Minitab, DataLyzer etc i can see that %Bias is always calculated and shown to the user. From my knowledge (quoting from AIAG MSA 4th Edition), in order for us to know whether bias is acceptable or not there are 2 ways,

1. if the p-value associated with the t-statistic bias is less than 0.05, or

2. if zero is between the lower bound and upper bound of bias confidence interval. (i may not phrase it correctly).

So my questions are:

Question 1: why are we calculating % bias here if we are not using it to evaluate the acceptance of Bias?. From my google search, i can't even find the acceptance criteria for this %bias at all...

Question 2: I took the example from AIAG MSA 4th edition whereby they have 15 data (5.8 , 5.7 , 5.9, 5.9, 6, 6.1, 6, 6.1, 6.4, 6.3, 6, 6.1, 6.2, 5.6 and 6) and then i calculated the p-value associated to t-statistic bias. I obtained t-statistic as 0.1217 and the associated p-value as 0.9048

So, if we are using criteria 1 from AIAG MSA which says that bias is acceptable if p-value less than 0.05 which in this case it is not so my earlier conclusion was this bias was clearly not acceptable.

However i further calculated the lower bound and upper bound confidence interval and i got the lower bound as -0.1107 and upper bound as 0.1241. Zero clearly lies between this lower and upper bound which means if we follow criteria 2 the bias study is acceptable.

In the very same AIAG book they mentioned this bias study is acceptable because of criteria 2 but they never mentioned anything about p-value.

So my real question is, does this means every single time when i do bias study i must check for these 2 criterias and if whichever pass that means bias study passed and if both of criteria failed only then i can conclude that this bias study failed?.