Re: Prediction

["Ian Schoeman" <ianschoe@worldonline.co.za>]

Grant Blair writes:

> When a process is in control, it is behaving in a sustained random manner,
> and the subsequent points are unpredictable. This comes from observing
> Deming's funnel experiment
> Processes which are out of control are predictable. Sooner or later, 
> there
> will be additional points out of control, even if common cause may make it
> appear that the process is within control limits for a short period of 
> time.
I am not sure if I agree fully with this statement.  I would have thought 
that 'in control' means the total absence of assignable cause of variation 
so that the process output becomed predictable.  Out of control IMHO means 
you can never be sure what yo are going to get or when the next assignable 
cause creeps in to increase variation.

You thoughts?

p.s. My condolences to all those victims of Katrina and to all those who 
have loved ones there.


Ian Schoeman