https://ij-healthgeographics.biomedcentral.com/articles/10.1186/1476-072X-7-50
https://ij-healthgeographics.biomedcentral.com/articles/10.1186/1476-072X-7-51
https://ij-healthgeographics.biomedcentral.com/articles/10.1186/1476-072X-7-49