[1] McMaster Univ, Med Ctr, Hamilton, ON L8N 3Z5, Canada
[2] Hamilton Civ Hosp, Henderson Res Ctr, Hamilton, ON, Canada
[3] Stanford Univ, Med Ctr, Stanford Stroke Ctr, Palo Alto, CA 94304 USA
[4] Duke Univ, Med Ctr, Duke Clin Res Inst, Durham, NC USA
[5] Ist Regina Elena, Dept Clin Epidemiol INFORMA, I-00161 Rome, Italy