The calculation of dementia or assignment of dementia status follows the Langa-Weir approach as applied to the sister study to the English Longitudinal Study of Ageing, namely the US Health and Retirement Study. This way, both studies are likely to give comparable results.
A cartogram map is the equivalent of a choropleth map with the size of the areas (local authority districts) is adjusted according to the prevalence of dementia. In this way, areas with higher prevalence are not only darker but also increased in size. Conversely, areas with lower prevalence are shrunk in size. The legend identifies three ranges: up to 5%, up to 10% and up to 15%.