Study Population and Health Outcomes

We obtained mortality data from the Massachusetts Department of Public Health for the years 2001 to 2015. The data include the coordinates of the residential address, date of death, place of death, and underlying cause of death based on the International Classification of Diseases, Tenth Revision (ICD‐10). We identified causes of death as follows: CVDs (ICD‐10: I00–I51), myocardial infarction (MI; ICD‐10: I21–I22), stroke (ICD‐10: I60–I69), and all‐cause nonaccidental total death (TOT; ICD‐10: A00‐R99). Because of the sensitive nature of the data collected for this study, requests to access the data set from qualified researchers trained in human subject confidentiality protocols may be sent to the Massachusetts Department of Public Health at https://www.mass.gov/orgs/department‐of‐public‐health. This study was approved by IRB‐20222 at Harvard University. Informed consent was not required because all subjects are deceased.

We excluded mortality of those aged <18 years, and we also stratified the population into different age groups: ≥18 years, 18 to 65 years, 65 to 85 years, and ≥85 years.

We converted the residential address coordinates to the corresponding ZIP code tabulation areas (ZCTAs), and we considered the ZCTA as the spatial unit of analysis, given that the confounders in our models are census variables that are tabulated at the ZCTA level. We then aggregated deaths for each of the above causes by year and by ZCTA. In the analysis by age groups, we calculated the annual death count for each mortality cause, for each age group, each ZCTA, and each calendar year.

This study was approved by the Human Subjects Committee at Harvard T.H. Chan School of Public Health and by the Massachusetts Department of Public Health.