FW: Ford and ranking

[WMack <WMack@PEC.com>]

I am not sure that I agree with the assertion that control charts support 
ranking and categorizing either people or objects.  

The purpose of a control chart is to: provide an indication that 
investigation of a process is justified, or to provide an indication
whether a change to a process has had the desired affect.  As the
control chart is a time ordered sequence of sampled results of a
process, it is hard to draw any conclusions as to why whatever 
is represented by a single point lies where it does.  It certainly
does not indicate any intrinsic quality about specific items.

There may be reasons to categorize people or things, but 
control charts are not one of them.

Wayne Mack