support the idea

[Nam-Ky Nguyen]

Dear John,

It seems you me the type of database you mentioned
will be more useful to combinatorial mathematicians
than to experimenters. Experimenters can't distinguish
between the A-efficiency and E-efficiency of an IBD.
However, they can distinguish an IBD and a row-column
design. The latter is more appropriate their
experiments as in reality heterogeneiy are in two
directions not one. 

There are other things I consider more important than
the database such as the tighter bound for
(alpha-resolvable) IBDs which are not BIBD and bound
for RCDs and I am quite sure that here is the area
combinatorial mathematicians can contribute.

Regards,

> Does it make much difference? In some cases yes, in
> others no. A-efficiency is a 
> 1-dimensional measure of design worthiness that can
> miss many pertinent aspects 
> of design behaviour. Might the collection of
> contrast variances for one of the 
> competing designs be more disperse than that of
> another? Might one enjoy a clear 
> advantage over another in terms of minimizing its
> worst variance (usually called 
> the E-criterion)? Might one be more robust to loss
> of plots or blocks? Might one 
> possess a variance/covariance matrix for treatment
> effects that better aligns 
> with underlying treatment structure than another?
> These are just some of the 
> questions that can be addressed if one has a
> collection of designs and 
> associated criteria values available. 
> 
> Putting these questions aside, any one or all three
> of the designs you mention 
> can be in the database, accessible via a few mouse
> clicks. This seems very smart 
> to me. Why ever search more than once? Get the
> design and store it. If someone 
> else wants to come up with a better (in some sense)
> design, then they can store 
> that in the database, too. They will all be there,
> online, accessible, and free.
> 
> Also, let us not forget that this database is about
> much more than statistical 
> aspects of design. It will contain *many* block
> designs for reasons ranging from 
> direct combinatorial interest to the need for a
> design in the construction of 
> other designs to much more. The current external
> representation lays out the 
> basic idea set, which will surely grow and change in
> the weeks to come.
> 
>

=====
Nam-Ky Nguyen, Ph.D.
Design Computing
email: nkn at designcomputing.net 
web:   www.designcomputing.net