ABSTRACT
Introduction Chapter 1 identified the significant international and European variations in stroke incidence and outcome. The factors that drive these differences are likely to be complex, as they are affected by the age, sex and social struc ture of the populations, differences in risk factor profiles, differences in healthcare systems and the ways in which individual patients are treated. Some of the apparent variation may reflect problems with data collection. If the definitions of the variables across centres and countries being com pared are open to interpretation, then systematic bias could be introduced.
