# [R] how to generate and evaluate a design using Algdesign

S Ellison S.Ellison at lgc.co.uk
Fri Oct 12 12:59:46 CEST 2007

```If you do something like length(coef(lm(y~.+v3:v4 + v5:v6, data=dat)))
to get a quick empirical estimate of required number of coefficients,
you will find that you have 35 coefficients, so 32 observations cannot
provide a solution at all. And indeed, nTrials=35 is the first size at
which optFederov even tries to find a design.

After that,many possible trial designs will be singular because (I
think) most subsets of the data will miss out support points for the
design. You need a lot of repeats to find a design at all with so few
points, or optfederov won't find a viable design at all.

If you're prepared to wait a while, run with at least nTrials=45 with
plenty of repeats and you have a chance of something useful, though the
efficiency (judged by Ge) looked pretty poor.

Steve E
>>> "sun" <flyhyena at yahoo.com.cn> 10/10/2007 14:59:59 >>>
Hi,

I have some problems when using AlgDesign->optFederov() generating
designs.

I have 6 variables, all factors. 3^2 and 4^4, I want to have a design
that
can take care of  main effects and two interactions within 2 pair of
variables v3-v4 and v5-v6, the following is the code

################
require(AlgDesign)
set.seed(1)
levels = c(v1=3,v2=3, v3=4,v4=4,v5=4,v6=4)

dat<-gen.factorial(levels,center=FALSE,varNames=names(levels),factors=
c(1,2,3,4,5,6))

model = ~.+v3:v4+v5:v6

optDgn<-optFederov(model,dat,nRepeat=5,nTrials = 32,criterion = "D",
approximate = F)

----------------------------
this lead to a error msg " nTrials must be greater than or equal to
the
number of columns in expanded X" . I thought I do not have that many
columns. if I change approximate to T, this error has gone.

if I remove nTrials argument in function call:
> optDgn<-optFederov(~.+v3:v4+v5:v6,dat,nRepeat=5,criterion =
> "D",approximate = F)
I got a error : "Singular design."

what would be the cause and what is the sullotion?

another question is, how do I measure or evaluate a design to see if it
is
able to handle which effects(main effects/which intercations)? I got
some
other designs generated by other packages, so I 'd like to check their

characteristics.

Sun

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