Re: The rationale for substantive knowledge of underlying process

[Kromkowski@aol.com]

<< I'd disagree to the extent that in order to plan for rational sub-grouping
 some process knowledge is necessary.  One needs to understand enough to
 know how various sub-grouping possibilities would be implemented to put
 together a sensible set of limits for a given process.>>

This, of course, would not apply to the U/C charts, the P/NP charts and the 
IndX/Mr chart.  (When in doubt, the IndX/Mr is not going to lead one to 
astray.) I suppose also as an attorney who routinely cross-examines "experts" 
and as a consequence has developed a tiny bit of contempt for "expertise," 
rational subgrouping is also not rocket-science, it's just being rational!  
Moreover, if you do it truly wrong, and the underlying substantive knowledge 
is truly that important, a signal of special cause will emerge and then 
substantive expertise should find the problem of grouping in its 
"investigation"; again, at a different stage from the construction and 
evaluation of the chart.

>> There are probably other exceptions to JDK's generalization as well.<<

The existence of exceptions, sounds like good evidence that my generalization 
is probably well taken!

>> Generally substantive knowledge can also be quite helpful in helping
 engineers, managers, supervisors, etc., understand what a given chart does
 or does not reveal. >>

Well, we disagree.  What a chart reveals is what it reveals; namely, signals 
to do investigation with armed with a very good idea of the separation of 
special cause variation from common cause variation.  The "investigation" of 
the signals, of course, does require substantive knowledge as well as the 
plan and implementation of ideas for improvement; but these are at different 
stages.

>> Also it is helpful in understanding the measurement processes and some 
beginning notion as to its capability.>>

Different stages in the cycle of improvement, to my way of thinking about it.

JDKromkowski