1. National Center of Epidemiology and CIBERNED, Carlos III Institute of Health; Madrid Spain
2. Department of Neurology; P. J. Safarik University; Kosice Slovakia
3. Department of Neurology; University Hospital of L. Pasteur; Kosice Slovakia
4. Department of Statistics; Center of Human and Social Sciences, Spanish Council for Scientific Research; Madrid Spain
5. Department of Neurological Sciences; Rush University Medical Center; Chicago Illinois USA