Why are some counties colored gray, meaning insufficient data?
Counties were considered to have insufficient data for calculation of a reliable death rate for a particular racial or ethnic group if the total number of deaths in the county and its contiguous neighboring counties was fewer than 20 during the rating period (heart disease 1991–1995 and 1996–2000; stroke 1991–1998). To avoid calculating rates for counties that 1) had nobody from a particular population living there, and 2) did have neighboring counties with significant numbers of the population, rates were also not calculated for counties with a population of less than 5 during the same span of years.
