TABLE 2—
Descriptive Statistics of Southern Counties Sampled for Hookworm by the Rockefeller Sanitary Commission (RSC), 1911–1914
| Dependent Variable | Mean or Proportion (SD) |
| County in RSC sample, % | 59.40 |
| County hookworm infection rate, % | 38.40 (25.72) |
| Proportion of RSC-participating counties, by state | |
| Alabama | 0.06 |
| Arkansas | 0.08 |
| Georgia | 0.12 |
| Kentucky | 0.04 |
| Louisiana | 0.09 |
| Mississippi | 0.13 |
| North Carolina | 0.17 |
| South Carolina | 0.05 |
| Tennessee | 0.10 |
| Texas | 0.05 |
| Virginia | 0.10 |
| Total | 1.0 |
| County-level environmental characteristics | |
| Frost-free d/y | 219.73 (36.46) |
| Particle size, cm | 0.15 (0.06) |
| Temperature, °F (5-y average of annual means) | 61.78 (4.12) |
| Precipitation, in (5-y average of annual totals) | 47.93 (7.56) |
| Elevation, meters | 163.73 (153.82) |
| County-level population characteristics | |
| Proportion Black | 0.33 (0.24) |
| Population/mile2 | 51.11 (74.29) |
| Population | 22 616.24 (21 625.40) |
| County-level program effects | |
| Proportion of children attending school | 0.57 (0.08) |
| Counties in early-adopting states | 34.2 |
| No. of mills | 1.07 (3.24) |
| Year of RSC infection survey | 1912.90 (0.99) |
| County-level soil pollution risk | |
| Sanitary index | 7.01 (5.73) |
| Improved acreage | 112 104.22 (67 782.26) |
Note. Total may not total 1.0 because of rounding.