TABLE 3—
Two-Stage Selection Model of Rockefeller Sanitary Commission’s Sampled Counties and Reported Hookworm Rates in the Counties Sampled, 1911–1914
| Stage 1: Odds That County Is in RSC Sample,OR (95% CI) | Stage 2: Hookworm Infection Rate,b (SE) | |
| State (Ref: Virginia) | ||
| Alabama | … | 1.47 (4.97) |
| Arkansas | … | 2.28 (4.73) |
| Georgia | … | 18.07*** (5.04) |
| Kentucky | … | 29.44*** (5.13) |
| Louisiana | … | 13.70* (6.01) |
| Mississippi | … | 11.88 (6.53) |
| North Carolina | … | 5.98 (4.56) |
| South Carolina | … | 3.31 (5.08) |
| Tennessee | … | 26.08* (3.98) |
| Texas | … | 4.90 (6.23) |
| Environmental characteristics | ||
| Frost-free, d | 1.004 (0.99, 1.01) | 0.16** (0.05) |
| Particle size | 0.04* (0.003, 0.70) | 310.94*** (21.94) |
| Temperature | 0.96 (0.92, 1.01) | 0.58* (0.30) |
| Precipitation | 1.04*** (1.02, 1.06) | −0.04 (0.15) |
| Elevation | … | −0.002 (0.007) |
| Population characteristics | ||
| Proportion Black | 2.70* (1.20, 6.07) | −11.30* (4.42) |
| Log population density | 6.65* (1.19, 37.1) | −10.20** (3.59) |
| Log population density squared | 0.64*** (0.51, 0.82) | … |
| Log population | 2.37*** (1.72, 3.25) | 7.30* (3.01) |
| Program effects | ||
| Log school attendance | 7.36** (2.25, 24.1) | … |
| County in early adopter state | 2.41*** (1.62, 3.58) | … |
| No. of mills (1913) | 1.12** (1.03, 1.21) | −0.98*** (0.25) |
| Year of RSC infection survey | … | −5.46*** (0.76) |
| Soil pollution risk | ||
| Sanitary index | … | −0.64*** (0.16) |
| Log improved acreage | … | −8.01*** (1.50) |
| Intercept | … | 88.87** (28.63) |
| Hazard | … | 8.47 (11.70) |
Note. CI = confidence interval; OR = odds ratio; RSC = Rockefeller Sanitary Commission. For stage 1, n = 984; c2 = 200.22; df = 11. For stage 2, n = 584; adjusted R2 = 0.63.
*P < .05; **P < .01; ***P < .001.