[1] Carlos III Inst Hlth, Natl Ctr Epidemiol, Unit Neuroepidemiol, Madrid, Spain
[2] Royal Free Hosp, Sch Med, Dept Neurosci, London, England
[3] Natl Hosp Neurol & Neurosurg, London WC1N 3BG, England
[4] IRCCS San Raffaele Roma, Dept Neurol, Rome, Italy
[5] Med Coll Georgia, Augusta, GA 30912 USA
[6] Klinikum Bremerhaven Reinkenheide, Dept Neurol, Bremerhaven, Germany
[7] So Gen Hosp, Dept Care Elderly Gerontol, Glasgow G51 4TF, Lanark, Scotland
[8] Kings Coll London, Inst Psychiat, Dept Psychol, London WC2R 2LS, England
[9] Univ Hosp Lewisham, Dept Neurol, London, England
[10] Guys Kings & St Thomas Sch Med, Dept Neurol, London, England
[11] Osaka Univ, Grad Sch Med, Dept Neurol, Osaka, Japan
[12] Fukuoka Univ, Dept Neurol, Fukuoka 81401, Japan
[13] Camborne Redruth Hosp, Dept Med Care Elderly, Redruth, Cornwall, England
[14] Univ Naples Federico II, Dept Neurol, I-80138 Naples, Italy
[15] Tel Aviv Univ, Sch Med, Assaf Harofeh Med Ctr, Dept Neurol, Zerifin, Israel
[16] Univ Pisa, Dept Neurol, Pisa, Italy
[17] Kings Coll Hosp London, Dept Clin Neurosci, London, England
[18] UK Parkinsons Dis Soc, Div Res & Dev, London, England
[19] Royal Coll Nursing, Dept Nursing, New York, NY USA
[20] Emory Univ, Dept Neurol, Atlanta, GA 30322 USA
[21] N Tyneside Gen Hosp, Dept Med, N Shields, England
[22] St Thomas Hosp, Lane Fox Sleep Ctr, London, England
[23] Baylor Coll Med, Dept Neurol, Houston, TX 77030 USA
[24] Univ Hosp Lewisham, Kings Coll Hosp, Natl Parkinsons Fdn Ctr, Dept Clin Neurosci,Guys Kings & St Thomas Sch Med, London, England