Martin Maechler maechler at stat.math.ethz.ch
Mon Jan 23 18:08:20 CET 2006

```>>>>> "MM" == Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>     on Sat, 21 Jan 2006 09:33:20 +0100 writes:

>>>>> "BertG" == Berton Gunter <gunter.berton at gene.com>
>>>>>     on Fri, 20 Jan 2006 14:15:49 -0800 writes:

BertG> I'm not sure what you mean by a "fractional
BertG> factorial" design here.
^^^^
and Bert was right on target.
Please apologize for the following, which I'm now sure Bert
knows probably much better than me.

MM> it's a pretty well known term, in (at least some schools of)
MM> classical analysis of variance, e.g.
MM> in the famous "Box, Hunter^2" (1987) book which had a 2nd
MM> edition last year (Wiley), see also Doug Bates's nice account on
MM> http://finzi.psych.upenn.edu/R/Rhelp02a/archive/29768.html
MM> and the R package  "BHH2"  which is devoted to the book (2nd Ed).

MM> BHH2 has a function  ffDesMatrix()  for fractional factorial
MM> conf.design() function in the package of the same name which
MM> allows to construct ff designs (via different specifications).
MM> see e.g, http://finzi.psych.upenn.edu/R/library/BHH2/html/ffDesMatrix.html

BertG> In general, when dealing with complex designs of the sort you appear to be thinking
BertG> about, small orthogonal designs don't exist. You
BertG> might wish to look at the AlgDesign package to
BertG> generate an efficient design to estimate only main
BertG> effects.

BertG> -- Bert Gunter Genentech Non-Clinical Statistics
BertG> South San Francisco, CA

BertG> "The business of the statistician is to catalyze the
BertG> scientific learning process."  - George E. P. Box

MM> now, since you have this nice signature, maybe you should
MM> get the above book? ;-) :-)

which was supposed to be something like a joke;

I have no good excuse for my blunder:
It was Saturday morning,

Martin Maechler, ETH Zurich

>>> -----Original Message----- From:
>>> r-help-bounces at stat.math.ethz.ch
>>> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of
>>> Roberto Furlan Sent: Friday, January 20, 2006 12:37 PM
>>> To: r-help at stat.math.ethz.ch Subject: [R] fractional
>>>
>>> Hi, i need to create a fractional factorial design
>>> sufficient to estimate the main effects.  The factors may
>>> have any number of levels, let's say any number from 2 to
>>> 6.  I've tried to use the library conf.design , but i
>>> cannot figure out how to write the code.  For example,
>>> what is the code for a design with 5 factors (2x3x3x5x2)
>>> and only main effects not confounded?
>>>
>>> thanks in advance!  Roberto Furlan University of Turin,
>>> Italy

```