On 21/06/10 20:32, Aline Deschamps wrote:
Thank you for your mail and the attached documents.
You're most welcome :-)
I've read the article and I found it very interesting, but I have some
questions :
- The 5 steps in this article are for creating a choice set for one
respondent, are they?
Yes, that's correct.
- In this article, it is written : "When two or more alternatives having
the same combination of attributes levels appear in one question, it is
necessary to repeat step 4". Does that mean we have to test each
question and go back to the beginning of the step 4 if we are in this
type of case, e. g. re add a new random number to each design?
Yes, this is common to all conjoint studies where a fractional factorial
is generated by computer. So, to put it in CBC terminology, you examine
each choice set for duplicate alternatives.
- In the function "optFederov", they choose the model " ~. " , but if I
want to study the first order interactions between the different
attributes, should I choose the model " ~.^2 " ?
Don't know, sorry. I am just learning about this myself, and do not
claim to be expert. I have just printed out the AlgDesign manual and
will be reading it when I get sick of marking exams (10 down, 260 to
go!). So, while I may be able to answer this question eventually, it
might be next week ...
- Finally, I need to make sure that the following condition : "every
respondent has to see, for all attributes, each of its levels
approximately the same number of times", is verified in my design. Is it
the case with that method? I'm not really sure...
Nor am I. I think D-Optimality measures that, but I can't swear to it.
I won't be able to work on this for the next few days, but am certainly
willing to share any solutions I've found to our common problems in the
future. Would you let me know if you find the answers? Perhaps we
should be having this discussion on-list? (I've assumed "yes", so have
CC-ed R-Help.)
Cheers,
John
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