For example, the definition of stroke usually encompasses ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage mainly because in the era before computed tomography it was impossible to distinguish between these diagnoses. Yet these distinct entities have unique risk factors and different prognoses. Transient ischemic attacks may or may not be included in the definition of stroke used to determine the incidence, prevalence, and mortality of cerebrovascular disease. Incidence rates, prevalence, and mortality rates are the basic components of the epiderniologic assessment of stroke within a population. While death certificates yield the most readily available data, mortality is not synonymous with incidence and may be affected by a number of variables.
Incidence measures the number of new cases of disease in a given time period.
Prevalence, the measure of existing cases at a particular point in time, a more germane measure of the burden of stroke on society, can be difficult to gauge. Finally, data from large cohorts may lead to skewed generalizations. The information is relevant to the defined populations, traditionally middle-aged white men, but cannot necessarily be generalized to other racial and gender groups. To rectify this gap, several studies now collect data from specific gender and minority groups. These Internet-based data sets were searched by ICD9 codes for information on mortality and disposition after ischernic stroke and intracerebral hemorrhage.