If you are trying to estimate the variance from a range, or a group of ranges, use d2*, but if you are trying to estimate a standard deviation, use d2. The d2 number should actually be used instead. It will show up especially in the attempt to determine reproducibility, where it is generally quite significant. When you use this constant to estimate a standard deviation, you get a biased result. I recommend doing some simulation work, and then you will discover a few things.ġ) The use of the d2* constant was developed for variances. Anyone who has ever used the AIAG methods and found that they can solve unsolvable problems knows your writing in nonsense. Your writings are used as an excuse to avoid the hard work of getting an adequate measure by a bunch of lazy MBB's and others. you think that industry just cares about control charts.

The problem with your rant is you have no way to deal with the adequacy of a measure where there is a specification. Wow, you must be a genius!Īnd your talking down to us about a + b does not equal c is just plain arrogance. So your 'honest' method just squared the result. It was 1962 and the error involved with doing calculations by hand was greater than the error with using r-bar to estimate s (or s^2). It is time for it to stop.įirst, if you've done your homework you understand why Standard Deviation, not variance was used at the onset of Gauge Studies. Don, I respect your work especially your SPC text, but your continued rant about the AIAG method is dishonest.

Gage rr minitab