Developer of XmR chart - Wheeler thread

[Paul Hollingworth <PH@4GM.com>]

EJBeach@aol.com writes
> There is no references in Don Wheeler's books on the individual and 
> moving range chart.
I beg to differ.
Dr Wheeler is a great advocate of XmR charts. There are extensive 
references to control charts for individuals in both 'Understanding 
Statistical Process Control' and 'Advanced Topics in Statistical Process 
Control' (just look in the index!). Throughout his entire book 
'Understanding Variation' Don uses XmR charts.

I regret that I cannot identify who the 'inventor' of the chart was, but 
Don Wheeler has certainly been instrumental in promoting its use. I 
vaguely recall Don once telling me that he had discussed the XmR chart 
with Dr Deming who was amused to recognise that it was a chart for both 
attributes and variables.

I find the XmR chart the best place to get people started. Unlike 
attribute charts it is hard to use it badly.  Novices can easily draw 
the chart by hand and understand how the limits are derived as the 
concept behind the formula is simple to understand.  In most cases they 
will then move on to use PC packages for creating charts - but at least 
they understand how the XmR chart works.

Incidentally one should take care to check how limits for Individuals 
charts are calculated in PC packages. I know of one (otherwise 
excellent) statistical package that offers individuals charts with 
limits drawn at 3 standard deviations (calculated as a single pass 
through the x values). This is NOT an XmR chart!

Regards
Paul H

--
Paul Hollingworth                       4GM Consulting
email: PH@4GM.com                       http://www.4GM.com
phone: +44(0) 1423 322225               fax: +44(0) 1423 322205