Statistics - the answer
I got a very quick response on this by using the AIAG website.
Submitted question:
Rev. 3, p. 134:
"d" is an estimate of the width of region II areas and, thus, an estimate of the GRR=5.15xSDgrr" d= 0.0237915
How do they make the jump to %GRR = 24% ?
(10/29/02 Errata changes it to 29%, I know, but I still can't figure the math here.)
Answer:
The d=0.0237915 is the 5.15 * std dev(GRR). To determine the %GRR we need (1) to determine the std dev (GRR) and the process/target std dev. Since the process variation exceeds the tolerance we use the estimated std dev based on the tolerance = 6 * std dev. The tolerance range is .095 (this was not given in the
example). Putting the pieces together yields a GRR percent of 29% = (100%)*std dev (grr)/std dev (target std dev) = (100%)*(0.0237915/5.15)/(.095/6).
This worked out exactly.