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Summary statistics of control variables for the 3104 counties in the study.
| Variable | Mean (SD) | Min | Max |
| Population aged ≥85 years (%) | 2.3 (0.01) | 0.0 | 8.0 |
| Non-Hispanic White (%) | 83.3 (0.16) | 5.1 | 99.8 |
| Voted for democrats (%) | 36.9 (0.17) | 3.1 | 82.1 |
| Household income (US $1000) | 89.2 (20.0) | 36.5 | 243.8 |
