luisfrpereira
21st December 2006, 10:15 AM
Hello.
I am a student finishing a degree in industrial engineering.
I would like to know the formulas to calculate the factors d2 an d3 used to build Xbar-R and X-mR charts.
Is there a book where this formulas are writen? I have tried a few they all have a table and no formulas...
:thanks:
Tim Folkerts
21st December 2006, 10:44 AM
On the right side of the page is a link to the NIST Engineering Statistics Handbook, which gives the equations (which can be rather ugly).
The direct link to the page with the information you want is I believe http://www.itl.nist.gov/div898/handbook/pmc/section3/pmc321.htm
Tim F
luisfrpereira
21st December 2006, 01:12 PM
Thank you for your help, but that is not what i needed.
The NIST Engineering Ststistic Handbook only has the formula for c4 factor ( in this page (http://www.itl.nist.gov/div898/handbook/pmc/section3/pmc32.htm#C4) ).
I am searching for the formulas for d2 and d3 factors.
:)
Bev D
21st December 2006, 02:07 PM
you will regret this but they are attached.
these formulas are just one reason why you should use the standard deviation and NOT the RANGE when n >10.
The other of course is that the standard deviation is a better estimator than the range and with computers it's easier to calculate. (at least it's fewer keystrokes in excel!)
Tim Folkerts
21st December 2006, 02:18 PM
I thought from a quick reading that the derivations for d2 and d3 were also there, but that apparently that was just for X-S charts, not X-R charts. If the NIST handbook doesn't have the equations, then I don't have any other good ideas. Sorry. :(
There was a reference listed that could be helpful (if you and find it).
Tim F
luisfrpereira
21st December 2006, 05:43 PM
Thank you Bev D for your help. That was almost all I am looking for.
In the formulas you gived not all variables are labeled. I belived that d2 and d3 only depended of the sample size (n). In the d2 formula what is the variable x? In the d3 formula what are the variables x, x1 xn and N ( since n = sample size ) ? :bonk:
One more thing, I would like to have a reference about this subject in my assignment's bibliography. Is there a book or paper about this subject?
:thanx:
Bev D
22nd December 2006, 12:42 PM
I believe it's in Quality Control and Industrial Statistics, by Acheson J. Duncan, published by Richard D Irwin; 5th edition (June 30, 1986)
sorry I can't help with the questions regarding the formulas. I dont' need to use them as I always use the standard deviation for large sample sizes. there is a table of d2 and d3 values that goes up to n=100 (by 5's in the higher sample size range) in Grant and Leavenworth's Statistical Quality Control.
