The methodology for calculating census tract level lead risk scores was developed by the Washington State Department of Health in order to identify which geographic populations have a greater risk of lead poisoning. The model combines Census housing and poverty data to calculate a lead risk score for each census tract and then maps the scores as deciles from 1 to 10, where 1 is the lowest risk and 10 is the highest risk. Vox.com worked with one of the chief epidemiologists responsible for developing the Washington State Department of Health's methodology, Rad Cunningham, to replicate the methodology nationally. To learn more about this methodology visit technical documentation https://s3.documentcloud.org/documents/2644455/Expert-Panel-Childhood-Lead-Screening-Guidelines.pdf