Neurologic and neuropsychiatric disorders are of great importance to societies and they also raise special considerations in epidemiological research methodology. Not only do neurologic and neuropsychiatric disorders form a major group of disorders associated with ageing populations, but those disorders that occur in earlier life can be associated with severe individual, family, and societal distress and burden. The inter-relationship of syndromes and disorders is a topic of major interest and growing biological insights across psychiatry and neurology. This includes not only overlaps in neurodegenerative syndromes but also those related to other systems such as metabolic, inflammatory, immune and vascular disorders.
