[1] Univ Auckland, Clin Trials Res Unit, Sch Populat Hlth, Fac Med & Hlth Sci, Auckland 1, New Zealand
[2] Auckland Hosp, Dept Neurol, Auckland, New Zealand
[3] Univ Utrecht, Dept Neurol, Rudolf Magnus Inst Neurosci, Med Ctr, Utrecht, Netherlands
[4] Univ Utrecht, Julius Ctr Hlth Sci & Primary Care, Med Ctr, Utrecht, Netherlands
[5] Univ Oxford, Nuffield Dept Clin Med, Clin Trial Serv Unit, Oxford, England
[6] Univ Oxford, Nuffield Dept Clin Med, Epidemiol Studies Unit, Oxford, England