I think that there is an understandable wish to have the simple orthogonal plans (and be it only for non-experts to be able to analyse the results themselves). For mixed levels, there is e.g. the L36 that should be able to accomodate plans like 2x2x2x3x3x3. Unfortunately, R is not very strong in this arena.
If I had more time, I would think about writing a package on comfortably designing experiments supported e.g. by the catalogues of Chen, J., Sun, D.X., and Wu, C.F.J. (1993). (A catalogue of two-level and three-level fractional factorial designs with small runs. International Statistical Review 61, 131-145.) Such a package should also provide the analysis facilities for any design generated with it, once it has been enriched with observed data. (This is a bit different from the typical R spirit, where users are often required to be experts themselves.) If anyone is planning a project like this or wants to make a diploma student work on it I would be interested in contributing. For the moment, if you want to implement main effects plans of the orthogonal sort (e.g. a Taguchi-plan like the L36) you have to use books or tables published on the internet, if you don't want to use expensive software like SPSS - not very comfortable, but possible. For example, you can find the L36 - which would be able to accomodate your 2x2x2x3x3x3 - in http://www.itl.nist.gov/div898/handbook/pri/section3/pri33a.htm. With kind regards, Ulrike >In general, a "main effects design" need not be orthogonal -- the main >effects merely need to be estimable. The trick is to estimate them with good >efficiency, etc. I think you need to consult a local statistician for help >to understand what these statistical concepts mean. > >In your example you could cross the 2^(3-1) with the 3^(3-1) to produce an >orthogonal design to estimate main effects. But of course that's 72 runs, >which I don't think you would consider "small." As a previous poster >commented, there are orthogonal mixed level arrays ("Addleman", "Kempthorne" >"Youden" -designs are a couple of phrases to try googling on) which stem >from the 1960's. I doubt that, in general, they would satisfy your needs. > >I have not used the AlgDesign package myself. I suggest you direct questions >about it to the author/maintainer, Bob Wheeler. > >-- Bert Gunter >Genentech Non-Clinical Statistics >South San Francisco, CA > >"The business of the statistician is to catalyze the scientific learning >process." - George E. P. Box > > -----Original Message----- > From: r-help-bounces at stat.math.ethz.ch > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of > statistical.model at googlemail.com > Sent: Monday, January 23, 2006 12:20 PM > To: Berton Gunter; statistical.model at googlemail.com; > r-help at stat.math.ethz.ch > Subject: [R] R: fractional factorial design in R > > > Yes, you're right. For, say, a 3 x 5 design, one can do > this in as few as > 7 > runs -- but only in general by some version of > one-factor-at-a-time (OFAT) > designs, which are inefficient. It is easy, via, say > model.matrix() to > write a general function to produce these. But I think it's a > bad idea; more > efiicient algorithmic designs are better, IMO, which is why I > suggested > AlgDesign. You and others are free to disagree, of course. > > Hi Bert, > thanks for your suggestion. > However, let us say that i need a 2x2x2x3x3x3 design, which > should not be > too hard. > I've loaded AlgDesign, and i am aware now that gen.factorial > allows me to > create a full desing. But how to create a main-effects-only > factorial design > (orthogonal)? > I am still not able to produce what i need. The function > model.matrix.formula is not very clear... :( > > Could you please indicate which syntax should i use? I'd > really appreciate > your help. > > Thanks in advance, > > Roberto Furlan > University of Turin, Italy > > > ---------------------------------------- > La mia Cartella di Posta in Arrivo è protetta con SPAMfighter > 188 messaggi contenenti spam sono stati bloccati con successo. > Scarica gratuitamente SPAMfighter! > > ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
