# Bias formula in MSA 4th Edition vs 3rd Edition

J

#### John Koh

I noticed (rather late) that in the MSA 4th edition, in the Bias formula (Pg 94) for 95% Confidence Interval, the value d2/d*2 was removed as compared to MSA 3rd edition. However on page 95, on Table III-B, the value d2=2.326 is still seen although it is now not used in the formula for calculation? Why is this so?

Also in the 3rd Edition, it says that d2 tables are available in Appendix C, but in fact only d*2 tables are available.

Thanks

#### Stijloor

Super Moderator
A Quick Bump!

Can someone help??

Thank you very much!!

#### Rameshwar25

##### Quite Involved in Discussions
Dear Mr Koh
There are tow methods for calculations of Bias.
1. Independent Sample Method
2. Control Chart Method (Using data collected for stability study)

The calculation formula for repeatability standard deviation are as following:

In MSA 3rd Edition:
A. Independent Sample Method
Std Dev=Range Bar/d*2
B. Control Chart Method
Std Dev=Range Bar/d*2 (same)

In MSA 4th Edition:
A. Independent Sample Method
Std Dev=square root [summation of (x-xbar)^2/n-1]
B. Control Chart Method
Std Dev=Range Bar/d*2 (same)

Regards
Rameshwar

J

#### John Koh

Thank you Mr. Ramesh.

Just one more question.

Do you know the reason why AIAG decided to change the formula from A. Independent Sample Method (Std Dev=Range Bar/d*2) to Std Dev=square root [summation of (x-xbar)^2/n-1] in the 4th Edition?

John

#### Rameshwar25

##### Quite Involved in Discussions
Dear Mr Koh
I do not the reason why AIAG has changed it.

Regards
rameshwar