Arnaud,

you might take a look at Latent Class Analysis:

http://ourworld.compuserve.com/homepages/jsuebersax/

Regards,  Murray Jorgensen

Arnaud Trollé wrote:
> Thank you all for your help.
>
> Sorry, you're right Art, I've been too evasive, I should have begun by 
> defining the framework of my study :
> [...]

-- 
Dr Murray Jorgensen      http://www.stats.waikato.ac.nz/Staff/maj.html
Department of Statistics, University of Waikato, Hamilton, New Zealand
Email: [log in to unmask]                                Fax 7 838 4155
Phone  +64 7 838 4773 wk    Home +64 7 825 0441    Mobile 021 1395 862

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