Table 5.
Aggregation errors in measures of the accessibility of hospitals at the census tract level
| Absolute difference between accessibility measure obtained from CTCa and WBlc aggregation methods | Percentiles | |||||||
| Mean | 5% | 10% | 25% | 50% | 75% | 90% | 95% | |
| Shortest network distance | ||||||||
| Minimum network distance | 365.35 | 11.19 | 22.54 | 57.40 | 147.23 | 365.04 | 947.76 | 1,595.45 |
| Average distance to 3 closest services | 284.19 | 5.88 | 12.07 | 32.04 | 102.51 | 276.01 | 719.27 | 1,250.98 |
| Average distance to 5 closest services | 290.26 | 5.10 | 11.81 | 34.16 | 94.54 | 275.32 | 800.69 | 1,300.49 |
| Average distance to all services | 309.02 | 3.44 | 7.42 | 26.94 | 89.12 | 275.50 | 869.61 | 1,470.33 |
| Number of services within 500 metres | 0.04 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.06 | 0.34 |
| Number of services within 1000 metres | 0.07 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.26 | 0.50 |
| Number of services within 2000 metres | 0.14 | 0.00 | 0.00 | 0.00 | 0.00 | 0.15 | 0.47 | 0.77 |
| Shortest time distance | ||||||||
| Minimum time distance | 0.37 | 0.02 | 0.03 | 0.09 | 0.20 | 0.41 | 0.84 | 1.34 |
| Average distance to 3 closest services | 0.31 | 0.01 | 0.02 | 0.06 | 0.15 | 0.34 | 0.73 | 1.11 |
| Average distance to 5 closest services | 0.31 | 0.01 | 0.02 | 0.06 | 0.15 | 0.35 | 0.75 | 1.16 |
| Average distance to all services | 0.32 | 0.02 | 0.03 | 0.06 | 0.15 | 0.37 | 0.73 | 1.22 |
| Number of services within 10 minutes | 0.69 | 0.00 | 0.00 | 0.07 | 0.39 | 0.93 | 1.72 | 2.60 |
| Number of services within 20 minutes | 0.76 | 0.00 | 0.00 | 0.00 | 0.25 | 0.71 | 1.98 | 3.20 |
| Number of services within 30 minutes | 0.52 | 0.00 | 0.00 | 0.00 | 0.04 | 0.41 | 0.98 | 2.15 |
| Absolute difference between accessibility measure obtained from WDAb and WBlc aggregation methods | Mean | 5% | 10% | 25% | 50% | 75% | 90% | 95% |
| Shortest network distance | ||||||||
| Minimum network distance | 134.15 | 3.51 | 6.89 | 20.20 | 51.74 | 136.36 | 311.82 | 501.59 |
| Average distance to 3 closest services | 118.06 | 2.14 | 4.50 | 16.10 | 46.43 | 126.23 | 275.19 | 413.62 |
| Average distance to 5 closest services | 123.87 | 2.15 | 5.01 | 14.99 | 48.60 | 140.36 | 300.31 | 421.81 |
| Average distance to all services | 157.70 | 1.95 | 4.05 | 17.45 | 66.96 | 240.45 | 360.42 | 473.07 |
| Number of services within 500 metres | 0.02 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.03 | 0.12 |
| Number of services within 1000 metres | 0.04 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.08 | 0.22 |
| Number of services within 2000 metres | 0.08 | 0.00 | 0.00 | 0.00 | 0.00 | 0.05 | 0.22 | 0.40 |
| Shortest time distance | ||||||||
| Minimum time distance | 0.12 | 0.00 | 0.01 | 0.02 | 0.06 | 0.11 | 0.27 | 0.43 |
| Average distance to 3 closest services | 0.10 | 0.00 | 0.01 | 0.02 | 0.05 | 0.10 | 0.23 | 0.39 |
| Average distance to 5 closest services | 0.10 | 0.00 | 0.01 | 0.02 | 0.04 | 0.10 | 0.22 | 0.39 |
| Average distance to all services | 0.10 | 0.00 | 0.01 | 0.02 | 0.04 | 0.10 | 0.22 | 0.39 |
| Number of services within 10 minutes | 0.23 | 0.00 | 0.00 | 0.02 | 0.12 | 0.29 | 0.57 | 0.84 |
| Number of services within 20 minutes | 0.22 | 0.00 | 0.00 | 0.00 | 0.06 | 0.20 | 0.44 | 0.85 |
| Number of services within 30 minutes | 0.14 | 0.00 | 0.00 | 0.00 | 0.01 | 0.11 | 0.31 | 0.68 |
a Aggregation method based on census tract centroid (the least accurate method).
b Aggregation method based on the population-weighted mean of the accessibility measure for dissemination areas within census tracts.
c Aggregation method based on the population-weighted mean of the accessibility measure for blocks within census tracts (the most accurate method).