Where can I find Duncan's Tables (d2* and Degrees of Freedom) on the internet?

[Atul Khandekar]

QS9000 MSA manual referes to "Duncan's Table D3 for d2* ", to look up the degrees of freedom related to No. of parts, operators and trials. (See : Confidence Interval for Average and Range Gage Study)

Are these tables available for reference anywhere on the web?

Thanx,

-Atul.

[Rick Goodson]

Is there a reason you can not used the table on Page 29 in the MSA manual? It is straight from Duncan's book, 'Quality Control and Industrial Statistics'.

d2* is a modification of d2 that gives weight to the number of samples (subgroups) used to compute R-bar. If more than 20 subgroups are used the factor is almost identical to d2.

[Atul Khandekar]

I can't use it because it gives only d2* values and not Degrees of Freedom.

I use that table for calculations of R&R though.

-Atul.

[Rick Goodson]

The table is also available in Ott's Text, "Process Quality Control" ISBN 0-07-047923-2 as table A-11.

Unless you need 'absolute' accuracy you can etimate df from the formula
df ~ (.9)g(m-1).

ie:

g m table df calc df
6 2 5.5 5.4
10 3 18.4 18.0
15 3 27.5 27.0
10 5 36.5 36.0
20 7 105.7 108.0

Hope that helps.