Re: Noise ...

[John <jsdwd@ksc.th.com>]

on 8/4/01 9:00 pm, GrantBlair@aol.com at GrantBlair@aol.com wrote:


> << First, would it be correct to say that the noise is the datum points within
> the UCL and LCL ?>>
> This is correct- you are defining "noise" as Chance cause or Common cause
> variation which is within the UCL and LCL and system. The opposing term used
> is "signal", which is also know as Assignable cause or Special cause.  Points
> outside UCL and LCL indicate its presence. There are two types of Signals,
> a shift in level and an increase in variation. In both cases, it is the
> responsibility of the local workforce to find and correct both sources of
> variation. ( It may also be appropriate for the workforce to adjust the
> process for changes in Level.)
> It is important that Signals/Special causes are eliminated before attempting
> a further reduction in variation

In Statistical Method from the Viewpoint of Quality, Shewhart also discusses
the  need for output from the process that is within the limits to also be
seen as having  no particular pattern to it, in other words to look as
though it were produced by a random process.  While Mr. Blair is correct as
far as his comments go, there are other indicators of special causes that
included trends, zigzag patterns.  Dr. Lloyd Nelson wrote and excellent
Technical Aid in the Journal of Quality Technology some years ago on the
various tests for special causes using statistical control charts.

> Now, suppose you can reduce the variation... ideally, to the point where
> nearly all of your product is exactly on target. (This is another important
> property of the normal distribution).

This is not a characteristic of the normal distribution.  Producing
material close to the target is an economic nicety, not a statistical one.

> Our conclusion is that we can increase market share from 25% toward 50% as we
> reduce variation. Further increases are possible if we have learned enough
> about  our process along the way to adjust the target in an appropriate
manner. 

I don't know where these numbers come from.  It seems to me that the benefit
of variation reduction on market share attainment would be case specific and
market specific and changeable over time.

> Note also that this second case is MANAGEMENT's responsibility, not the
> workforce.

It's all management's responsibility.

John Dowd
jsdwd@ksc.th.com