# MSA bias calculation in 3rd edition - Why is d2/d2star used?

S

#### Stevenli

Dear all,

For bias in MSA 3rd edition, I have one question as following.
When calculate the 1-α confident interval (CI), there is one formula:

Bias+/-[d2σb(tv,1-α/2)/d2star]

The question is why d2/d2star is used, because when I check the traditional t distribute CI formula, there is no such kind of parameter.

Your attention would be highly appreciated.
Best regards
Steven

#### Marc

##### Fully vaccinated are you?
Any experts here have an answer for this post?

#### Wes Bucey

##### Prophet of Profit
It's a weekend. Many of our regular Covers take the weekend off and will return Monday. I'm sure some of the statistics whizzes will have an interesting answer.

J

#### jinzhoujun

Why not use T-test to test the bias in AIAG MSA

hi
in AIAG MSA , use d2 and d2* to calculate the range of bias ,rather than use T-test to test the bias
thanks

Last edited by a moderator:
A

#### Atul Khandekar

Stevenli said:
For bias in MSA 3rd edition, I have one question as following.
When calculate the 1-α confident interval (CI), there is one formula:

Bias+/-[d2σb(tv,1-α/2)/d2star]

The question is why d2/d2star is used, because when I check the traditional t distribute CI formula, there is no such kind of parameter.
jinzhoujun said:
hi
in AIAG MSA , use d2 and d2* to calculate the range of bias ,rather than use T-test to test the bias
thanks
My knowledge of statistics is rather limited so I won't be able to explain this esoteric stuff well. From whatever I've tried to research on the subject, here are a few links that MAY help.

From AIAG: StatExpose_d2.pdf

From Quality Engineering, Vol 13, No 2:
A Note on Using Ranges to Estimate Variability - by Woodall/Montgomery.
Moderator Note:
This can now be purchased from: http://asq.org/qic/display-item/index.html?item=14637

From iSixSigma Discussion forum: Bias Calculation

and

J

#### jinzhoujun

almost two years passed, we have no anwser,I think we did better put forwards this to AIAG, maybe it is mistake ,as i know they made mistake in other place,they mistake “g” for “ mg”.

J

#### jinzhoujun

Atul Khandekar ,thank you for your offer , I get answer now, in fact ,this is my question, I ask steven Li put forward it

G

#### Gagandeep S. Datta

I wanted to check on the statement - "as i know they made mistake in other place,they mistake ?g? for ? mg?.?

Is it that they mistake "g" for "m"?

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