[TCML] Re:One factor at a time? was: RSG disks - who can make them ?

["Kurt Schraner" <k.schraner@xxxxxxxxxxx>]

Ed Phillips wrote:
>    You cannot test anything at all if you alter more than 1 aspect at
> time!
>    This statement is worth a comment.  Not many engineers I know have
> learned that but it's very very important if you want to learn
> anything from an experiment.  One experiment with two variables is
> close to useless.
> Ed
>
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Hi Ed,

of course, I agree, especially if evaluating _known_ variables in their 
possibly nonlinear behavior, ...but not quite full hearted ;-)

During my jobtime, I had sometimes to do with the design and analysis of 
experiments for the chemical industry. Sometimes quite a number of 
variables(5..to 10?) were candidates for a response-function, and it was not 
known, which ones were significant...and which one might interact with one 
another. In those situations multivariate statistical analysis, with the 
goal of reducing the experimental work/cost is attained by variing different 
variables _simulaneously_, following statistically founded experimental 
design plans for the different levels of detail. Interpretation models at 
those levels are predominately simple linear or second order relationships. 
But, if the levels of the variables are choosen by good common sense, 
results can be convincing.

Literature: Design and Analysis of Industrial Experiments
           Owen L. Davies, Publ. by Oliver & Boyd, London, 1967

In electricity we are much more used to strong physics-law relationsships, 
than in chemical engineering. But a TC, despite it's few elements, presents 
a not quite easy to understand multivariable system, as i.e. is shown by the 
current thread of Ch.Swinson/J.Freau/B.Anderson. Part of it might be solved 
by the, hopefully not forgotten, Terry program:

http://drsstc.com/~sisg/files/scantesla/scantesla762.zip

...which tries to exhaust a wide variable space, by applying the known 
physics laws.

Best regards

Kurt



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