Dear Statalist,
Thank you very much for your valuable replies.
Dear Carlo, is there a reference supporting the temptative solution you recommended?
I sincerely thank you in advance,
Theo
      
___________________________________________________________ 
&KHgr;&rgr;&eegr;&sgr;&igr;&mgr;&ogr;&pgr;&ogr;&igr;&egr;&iacgr;&tgr;&egr; Yahoo!; 
&Bgr;&agr;&rgr;&egr;&thgr;&eeacgr;&kgr;&agr;&tgr;&egr; &tgr;&agr; &egr;&ngr;&ogr;&khgr;&lgr;&eegr;&tgr;&igr;&kgr;&aacgr; &mgr;&eegr;&ngr;&uacgr;&mgr;&agr;&tgr;&agr; (spam); &Tgr;&ogr; Yahoo! Mail 
&dgr;&igr;&agr;&thgr;&eacgr;&tgr;&egr;&igr; &tgr;&eegr;&ngr; &kgr;&agr;&lgr;&uacgr;&tgr;&egr;&rgr;&eegr; &dgr;&ugr;&ngr;&agr;&tgr;&eeacgr; &pgr;&rgr;&ogr;&sgr;&tgr;&agr;&sgr;&iacgr;&agr; &kgr;&agr;&tgr;&aacgr; &tgr;&ohgr;&ngr; &egr;&ngr;&ogr;&khgr;&lgr;&eegr;&tgr;&igr;&kgr;&ohacgr;&ngr; 
&mgr;&eegr;&ngr;&ugr;&mgr;&aacgr;&tgr;&ohgr;&ngr; http://login.yahoo.com/config/mail?.intl=gr 
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/